#include<bits/stdc++.h>
#define rep(i,a,n) for (int i = a;i < n;i++)
using namespace std;

int main() {
    int a; cin >> a;
    if(a < 15){
        cout << -1 << endl;
        return 0;
    }
    rep(i,2,100){
        if(a/i == 1 && a%i == 7){
            cout << i << endl;
        }
    }
}