#include <bits/stdc++.h>

#define forn(i, n) for (int i = 0; i < (int)(n); ++i)
#define for1(i, n) for (int i = 1; i <= (int)(n); ++i)
#define fore(i, l, r) for (int i = (int)(l); i <= (int)(r); ++i)
#define ford(i, n) for (int i = (int)(n) - 1; i >= 0; --i)
#define pb push_back
#define fi first
#define se second
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()

using namespace std;

typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<vi> vvi;
typedef vector<vll> vvl;
typedef pair<int, int> pint;
typedef vector<pint> vpint;
typedef double ld;

ll GCD(ll a, ll b) { return b ? GCD(b, a % b) : a; }
ll LCM(ll a, ll b) { return a / GCD(a, b) * b; }
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

int main() {
  int A;
  cin >> A;
  int ans = A - 7;
  cout << (ans < 8 ? -1 : ans) << endl;
  return 0;
}