#include "bits/stdc++.h"

#define debug(x) cout<<#x<<": "<<x<<endl
#define rep(i,n) for (int i=0;i<(n);i++)
#define FOR(i,a,b) for (int i=(a);i<=(b);i++)
#define all(a) (a).begin(),(a).end()
using namespace std;
typedef vector<int> VI;
typedef vector<vector<int>> VVI;
typedef long long ll;


void solve() {
#ifdef _WIN32
	istream &cin = ifstream("input.txt");
#endif

	ll n;
	cin >> n;

	if (n < 15) {
		cout << -1 << endl;
	} else {
		cout << n - 7 << endl;
	}
}




int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);


	solve();
	system("PAUSE");
	return 0;
}