#define _GLIBCXX_DEBUG
#define ll long long
#define INF 1000000000;
#define INF_B 1000000000000000000;
#include <bits/stdc++.h>
using namespace std;
using Graph = vector<vector<int>>;

int main(){
  int A; cin >> A;
  int ans;
  A >= 15 ? ans = A-7: ans = -1;
  cout << ans << endl;
}