#include <iostream>
#include <vector>
#include <algorithm>
#include <math.h>

#define ALL(x) (x).begin(),(x).end()
#define RALL(x) (x).rbegin(),(x).rend()
#define REP(i,a,n) for(int i = (a);i < (n);i++)
#define PI 3.14159265359
#define MOD 1000000007

using namespace std;

int main(){
    int a;
    cin >> a;
    REP(i,8,100){
        if(a/i == 1 && a%i == 7){
            cout << i << endl;
            break;
        }
        else if(a/i < 1){
            cout << -1 << endl;
            break;
        }
    }
    return 0;
}