#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <iomanip>
#include <stack>
#include <algorithm>
#include <string>
#include <map>
#include <iterator>
#include <set>
#include <queue>
#include <bitset>
#include <cassert>

using namespace std;


int main() {
    int A;
    cin >> A;
    for (int i = 2; i < 100; ++i) {
        if (A / i == 1 and (A % i == 7)) {
            cout << i << endl;
            return 0;
        }
    }
    cout << "-1" << endl;
    return 0;
}