#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<n;i++)
//#define int long long
using namespace std;

signed main()
{
	int A, X;

	cin >> A;

	X = A - 7;
	if (X > 0)
	{
		cout << X << endl;
	} else {
		cout << -1 << endl;
	}
}