#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;
using ld = long double;

int a;

int main() {
  cin >> a;
  for (int x = 8; ; x++) {
    int b = x + 7;
    if (a == b) {
      cout << x << endl;
      return 0;
    } else if (a < b) {
      cout << -1 << endl;
      return 0;
    }
  }
  return 0;
}