#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef pair<int, int> pii;
#define pb push_back
#define mp make_pair
#define fi first
#define se second

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