cf233B

#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
typedef pair< int, int > pii;

#define mod 1000000007
#define pb push_back

int sum( long long n ){
    int s= 0;

    while( n > 0 ){
        int r= n%10;
        n/= 10;
        s+= r;
    }

    cout << s << endl;

    return s;
}

int main(){

    long long n;
    long long l, h;
    bool flag= false;

    cin >> n;

    l= 1;
    h= sqrt( n );

    while( l <= h ){

        long long m= l + ( h-l )/2;

        long long r= 1ll*m*( m + sum( m ) );

        //cout << l << ' ' << h << ' ' << r << endl;

        if( r== n ){
            flag= true;
            cout << m << endl;
            break;
        }

        if( r < n )
            l= m;
        else
            h= m;

    }

    if( !flag ){
        cout << -1 << endl;
    }

    return 0;
}