#include<iostream>
#include <math.h>
#include <string>
#include <iomanip>
using namespace std;

int main(){
	int o;
	int answer;
	cin >> o;
	if (o < 15){
		answer = -1;
	}
	else{
		answer = o - 7;
	}

	cout << answer << endl;



	return 0;
}