BigInt Updated

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
using namespace std;

#define int long long
#define mp make_pair
#define pb push_back

#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("avx2")

constexpr int INF = (int)2e18;
constexpr int N = (int)4e5 + 111;
constexpr int md = (int)1e9+7;
constexpr int mdPower = (int)1e9+7 - 1;
constexpr double eps = 1e-7;

typedef __int128 _uint;
typedef long long ll;

mt19937_64 rnd(time(nullptr));

void add(int& a,int b){
    a += b; if(a >= md) a -= md;
}
void sub(int& a,int b){
    a -= b; while(a < 0) a += md;
}
void add(__int128& a,int b){
    a += b;
}
void sub(__int128& a,int b){
    a -= b;
}

int bpow(int a,int b){
    if(b == 0)
        return 1;
    if(b % 2 == 0){
        int t = bpow(a,b>>1);
        return 1ll*t*t%md;
    }
    return 1ll * a*bpow(a,b-1) % md;
}

int inv(int a){
    return bpow(a,md-2);
}

//int fac[N],invfac[N];
//
//void init(){
//    fac[0] = 1;
//    for(int i = 1; i < N; i++){
//        fac[i] = (fac[i-1] * i) % md;
//    }
//    invfac[N-1] = inv(fac[N-1]);
//    for(int i = N-2; i >= 0; i--){
//        invfac[i] = (invfac[i+1] * (i+1))%md;
//    }
//    return;
//}
//
//int C(int n,int k){
//    if(k > n)
//        return 0;
//    return fac[n] * invfac[k] % md * invfac[n-k] % md;
//}
//
//int A(int n,int k){
//    if(k > n)
//        return 0;
//    return fac[n] * invfac[n-k] % md;
//

struct BigInt{
    vector<int> v;
    BigInt(){}
    BigInt(string s){
        reverse(s.begin(),s.end());
        for(int i = 0; i < s.size(); i++)
            v.pb(s[i] - '0');
        if(v.empty())
            v.pb(0);
    }
    BigInt(int x){
        string s = to_string(x);
        reverse(s.begin(),s.end());
        for(int i = 0; i < s.size(); i++)
            v.pb(s[i] - '0');
        if(v.empty())
            v.pb(0);
    }
    bool operator <=(BigInt a){
        string s1 = "";
        for(auto& x : v)
            s1 += x + '0';
        while(!s1.empty() && s1.back() == '0')
            s1.pop_back();
        if(s1.empty())
            s1 = "0";
        reverse(s1.begin(),s1.end());
        string s2 = "";
        for(auto& x : a.v)
            s2 += x + '0';
        while(!s2.empty() && s2.back() == '0')
            s2.pop_back();
        if(s2.empty())
            s2 = "0";
        reverse(s2.begin(),s2.end());
        if(s1.size() < s2.size())
            return true;
        if(s1.size() > s2.size())
            return false;
        for(int i = 0; i < s1.size(); i++){
            if(s1[i] > s2[i])
                return false;
            if(s1[i] < s2[i])
                return true;
        }
        return true;
    }
    bool operator <(BigInt a){
        string s1 = "";
        for(auto& x : v)
            s1 += x + '0';
        while(!s1.empty() && s1.back() == '0')
            s1.pop_back();
        if(s1.empty())
            s1 = "0";
        reverse(s1.begin(),s1.end());
        string s2 = "";
        for(auto& x : a.v)
            s2 += x + '0';
        while(!s2.empty() && s2.back() == '0')
            s2.pop_back();
        if(s2.empty())
            s2 = "0";
        reverse(s2.begin(),s2.end());
        if(s1.size() < s2.size())
            return true;
        if(s1.size() > s2.size())
            return false;
        for(int i = 0; i < s1.size(); i++){
            if(s1[i] > s2[i])
                return false;
            if(s1[i] < s2[i])
                return true;
        }
        return false;
    }
    bool operator >(BigInt a){
        string s1 = "";
        for(auto& x : v)
            s1 += x + '0';
        while(!s1.empty() && s1.back() == '0')
            s1.pop_back();
        if(s1.empty())
            s1 = "0";
        reverse(s1.begin(),s1.end());
        string s2 = "";
        for(auto& x : a.v)
            s2 += x + '0';
        while(!s2.empty() && s2.back() == '0')
            s2.pop_back();
        if(s2.empty())
            s2 = "0";
        reverse(s2.begin(),s2.end());
        if(s1.size() < s2.size())
            return false;
        if(s1.size() > s2.size())
            return true;
        for(int i = 0; i < s1.size(); i++){
            if(s1[i] > s2[i])
                return true;
            if(s1[i] < s2[i])
                return false;
        }
        return false;
    }
    bool operator !=(BigInt a){
        return a.v != v;
    }
    void print(){
        string s = "";
        for(auto& x : v)
            s += x + '0';
        while(!s.empty() && s.back() == '0')
            s.pop_back();
        if(s.empty())
            s = "0";
        reverse(s.begin(),s.end());
        cout << s;
        return;
    }
    void read(){
        string s;
        cin >> s;
        v.clear();
        reverse(s.begin(),s.end());
        for(int i = 0; i < s.size(); i++)
            v.pb(s[i] - '0');
        if(v.empty())
            v.pb(0);
    }
};

void normalize(BigInt& a){
    while(!a.v.empty() && a.v.back() == 0){
        a.v.pop_back();
    }
    if(a.v.empty())
        a.v.pb(0);
    return;
}

BigInt operator +(BigInt a,BigInt b){
    BigInt c;
    int r = 0;
    for(int i = 0; i < max(a.v.size(),b.v.size() + 1); i++){
        int v1 = 0, v2 = 0;
        if(i < a.v.size())
            v1 = a.v[i];
        if(i < b.v.size())
            v2 = b.v[i];
        int s = v1 + v2 + r;
        r = s/10;
        c.v.pb(s%10);
    }
    while(!c.v.empty() && c.v.back() == 0)
        c.v.pop_back();
    if(c.v.empty())
        c.v.pb(0);
    return c;
}
BigInt operator -(BigInt a,BigInt b){
    BigInt c;
    int r = 0;
    for(int i = 0; i < max(a.v.size(),b.v.size() + 1); i++){
        int v1 = 0, v2 = 0;
        if(i < a.v.size())
            v1 = a.v[i];
        if(i < b.v.size())
            v2 = b.v[i];
        int s = v1 - v2 + r;
        r = s/10;
        c.v.pb(s%10);
    }
    for(int i = 0; i < c.v.size(); i++){
        if(c.v[i] < 0){
            for(int j = i+1; j < c.v.size(); j++){
                if(c.v[j] > 0){
                    c.v[j]--;
                    for(int t = j-1; t > i; t--){
                        c.v[t] += 9;
                    }
                    c.v[i] += 10;
                    break;
                }
            }
        }
    }
    while(!c.v.empty() && c.v.back() == 0)
        c.v.pop_back();
    if(c.v.empty())
        c.v.pb(0);
    return c;
}
BigInt operator *(BigInt a,BigInt b){
    BigInt c;
    c.v.resize(a.v.size()+b.v.size()+10,0);
    for(int i = 0; i < a.v.size(); i++){
        for(int j = 0;j < b.v.size(); j++){
            c.v[i+j] += a.v[i] * b.v[j];
        }
    }
    int r = 0;
    for(int i = 0; i < c.v.size(); i++){
        c.v[i] += r;
        r = c.v[i] / 10;
        c.v[i] %= 10;
    }
    while(!c.v.empty() && c.v.back() == 0)
        c.v.pop_back();
    if(c.v.empty())
        c.v.pb(0);
    return c;
}
BigInt pw10[21001];
BigInt operator/(BigInt a,BigInt b){
    if(a < b)
        return BigInt(0);
    BigInt c = BigInt(0);
    c.v.resize(a.v.size(),0);
    for(int i = a.v.size()-1; i >= 0; i--){
        for(int j = 0; j < 11; j++){
            if(c*b + pw10[i] * j * b > a){
                c.v[i] = max(0ll,j-1);
                break;
            }
        }
    }
    normalize(c);
    return c;
}
BigInt operator/(BigInt a,int b){
    return a / BigInt(b);
}
BigInt sqrt(BigInt x){
    BigInt l = BigInt(0), r = BigInt("1" + string(x.v.size()/2+1,'0'));
    while((r - l) > BigInt(1)){
        BigInt m = (l+r)/2;
        if(m * m > x)
            r = m;
        else
            l = m;
    }
    return l;
}

void init(){
    BigInt a = BigInt(1);
    for(int i = 0; i < 5001; i++){
        pw10[i] = BigInt("1" + string(i,'0'));
    }
    return;
}

void solve(){
    init();

//    (BigInt(50)/2).print();
//
//    return;
    BigInt P;
    P.read();
    BigInt tmp = sqrt(P);
    int len = tmp.v.size();

    for(int m = max(1ll,len-1); m <= len+2; m++){
        BigInt t = BigInt(m+1);
        BigInt u = t * t + 4*P;
        BigInt rt = sqrt(u);
//        cerr << "u = ";
//        u.print();
//        cerr << "\n";
//        cerr << "rt = ";
//        rt.print();
//        cerr << "\n";
        if(rt * rt != u){
//            cerr << "m = " << m << "\n";
            continue;
        }
        rt = rt + 1 - m;
        t = rt / 2;
        if(t * 2 != rt)
            continue;
        normalize(t);
        if(m != t.v.size()){
//            cerr << "t = ";
//            t.print();
//            cerr << "\n";
//            cerr << "v.sz = " << t.v.size() << "\n";
            continue;
        }
        t.print();
        return;
    }

    cout << "-1\n";

    return;
}

signed main(){
    ios::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr);
    int tests = 1;
//    cin >> tests;
    for(int test = 1; test <= tests; test++){
//        cerr << "test = " << test << "\n";
        solve();
    }
    return 0;
}
/**
dist = max(abs(x-x1),abs(y-y1))

3 - 2

**/