#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
  #include "settings/debug.cpp"
  #define _GLIBCXX_DEBUG
#else
  #define Debug(...) void(0)
#endif
#define rep(i, n) for (int i = 0; i < (n); ++i)
using ll = long long;
using ull = unsigned long long;

int main() {
  int n;
  cin >> n;
  int base = 8;
  while (true) {
    if (base + 7 > n) break;
    if (base + 7 == n) {
      cout << base << endl;
      return 0;
    }
    base++;
  }
  cout << -1 << endl;
  return 0;
}