#include <algorithm>
#include <cstdio>
#include <iostream>
#include <map>
#include <math.h>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
using namespace std;

#define ll long long
#define INF (1 << 30)
#define INFLL (1LL << 60)

int main() {
	int a;
	cin >> a;
	if(a <= 14){
		cout << -1 << endl;
	}else{
		cout << a - 7 << endl;
	}
	return 0;
}