UVA 11466 - Largest Prime Divisor

#include<bits/stdc++.h>
// #include <iostream>
// #include <cstdio>
// #include <cstdlib>
// #include <algorithm>
// #include <cmath>
// #include <vector>
// #include <set>
// #include <map>
// #include <queue>
// #include <ctime>
// #include <cassert>
// #include <complex>
// #include <string>
// #include <cstring>
// #include <queue>
// #include <bitset>

using namespace std;
typedef long long           ll;
typedef unsigned long long  ull;

#define ff                  first
#define ss                  second
#define pb                  push_back
#define mp                  make_pair
#define in                  insert
#define vi                  vector< int >
#define vll                 vector< ll >


#define f0(b)               for(int i=0;i<(b);i++)
#define f00(b)              for(int j=0;j<(b);j++)
#define f1(b)               for(int i=1;i<=(b);i++)
#define f11(b)              for(int j=1;j<=(b);j++)
#define f2(a,b)             for(int i=(a);i<=(b);i++)
#define f22(a,b)            for(int j=(a);j<=(b);j++)
#define RFOR(i,x,y)         for(int i=x;i>=y;i--)
#define unq(v)              sort(all(v)),(v).resize(unique(all(v))-v.begin())
#define all(v)              v.begin(),v.end()
#define rall(v)             v.rbegin(),v.rend()
#define reversed(s)         reverse(s.begin(), s.end())

#define testcase            ll t; cin>>t; while (t--)
#define vout(v)             for(int ind=0;ind<v.size();ind++){ cout<<v[ind]; if(ind<v.size()-1) cout<<' '; else cout<<endl;}
#define arrout(arr,i,x,y)   for(int i=x;i<=y;i++){ cout<<arr[i]; if(i<y) cout<<' '; else cout<<endl;}
#define READ()              freopen("input.txt", "r", stdin)
#define WRITE()             freopen("output.txt", "w", stdout)

#define sci(n)              scanf("%d",&n)
#define scii(x,y)           scanf("%d %d",&x,&y)
#define scl(n)              scanf("%lld",&n)
#define scll(x,y)           scanf("%lld %lld",&x,&y)
#define gtl(x)              getline(cin, (x))

#define PI                  acos(-1)
#define CLR(x, y)           memset(x, y, sizeof(x))
#define Precision(a)        cout << fixed << setprecision(a)
#define Flame()             ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0)
#define MAXP                1000006
#define MOD                 1e9+7//10000007
#define EPS                 1e-7

template <typename T> T Sqr(T x) { T n = x * x ; return n ;}
template <typename T> T Pow(T B,T P){ if(P==0) return 1; if(P&1) return B*Pow(B,P-1);  else return Sqr(Pow(B,P/2));}
template <typename T> T Abs(T a) {if(a<0)return -a;else return a;}
template <typename T> T Gcd(T a,T b){if(a<0)return Gcd(-a,b);if(b<0)return Gcd(a,-b);return (b==0)?a:Gcd(b,a%b);}
template <typename T> T Lcm(T a,T b) {if(a<0)return Lcm(-a,b);if(b<0)return Lcm(a,-b);return a*(b/Gcd(a,b));}
template <typename T> T BigMod (T b,T p,T m){if (p == 0) return 1;if (p%2 == 0){T s = BigMod(b,p/2,m);return ((s%m)*(s%m))%m;}return ((b%m)*(BigMod(b,p-1,m)%m))%m;}
template <typename T> inline string ToBinary(T n) {string r ;while(n != 0) {r = ( n % 2 == 0 ? "0" : "1" ) + r ; n >>= 1;} return r ;}
long long BinaryToDecimal(string s) {int len = s.size();long long n = 0, p = 1;for (int i = len - 1; i >= 0; i-- , p *= 2) n += p * (s[i] - '0');return n;}

int Strtoint(string str){stringstream ss(str);int x = 0;ss >> x ;return x ;}
string Intostr(int x){stringstream ss; ss << x; string str = ss.str(); return str;}

#define bug printf("**!\n")
#define DB(x) cout << #x << " = " << x << endl
#define DDB(x, y) cout << #x << " = " << x << "   " << #y << " = " << y << endl
#define DDDB(x, y, z) cout << #x << " = " << x << "   " << #y << " = " << y << "   " << #z << " = " << z << endl


int main()
{
   // Flame();
    ll n;
    while(cin >> n && n)
    {
        vector<ll> v;
        if(n<0)
        {
            n=n*(-1);
        }
        ll x=n;
        for(ll i=2; i*i<=n; i++)
        {
            if(x%i==0)
            {
                while(x%i==0)
                {
                    x/=i;
                }
                v.pb(i);
            }
        }
        if(x>1) v.pb(x);
        ll sz=v.size();
        if(sz<=1) cout << -1 << endl;
        else cout << v[sz-1] << endl;
    }
    return 0;
}