#include<cstdio>
#include<iostream>
#include<algorithm>
#include<string>
#include<queue>
#include<vector>
#include<functional>
#include<cmath>
#include<map>
#include<stack>
#include<set>
#include<numeric>

using namespace std;
typedef long long ll;
typedef pair<int, int> pi;
typedef pair<ll, ll> pl;

int main()
{
	int A;
	cin >> A;

	int ans = A-7;
	if (A <= 7 || A % ans != 7) {
		cout << -1 << endl;
	}
	else {
		cout << ans << endl;
	}
  return 0;
}