#define _CRT_SECURE_NO_WARNINGS
#include <cstdio>
#include <iostream>
#include <string>
#include <algorithm>
typedef unsigned long long ull;
using namespace std;
int main() {
	int A;
	cin >> A;
	// X+7==A
	// X>=8
	if (A < 15)cout << -1 << endl;
	else cout << A - 7 << endl;

}