#include <bits/stdc++.h>
using namespace std;

int main(){
	ios::sync_with_stdio(false);
	cin.tie(0);  
	int n;
	cin >> n;
	int x = n - 7;
	if(x < 8) {
		cout << -1 << endl;
	}
	else {
		cout << x << endl;
	}
	return 0;	
}