#include<iostream>
#include<string>
#include<algorithm>
#include<cmath>
#include<iomanip>
#include<cstring>
#include<map>
#include<vector>
#include<queue>
#include<climits>
using namespace std;
typedef long long int ll;

int main(){

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