#define _CRT_SECURE_NO_WARNINGS // #pragma warning(disable:4996)
#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
#include <functional>
#include <sstream>
#include <cmath>
using namespace std; 

#define rep(i,a,b) for(int i=(a);i<(b);i++)
#define pb push_back
#define mp(a,b) make_pair(a,b)
#define all(a) a.begin(),a.end()

typedef pair<int, int> Pii;
typedef vector<int> V;
typedef vector<V> VV;
typedef vector<VV> VVV;
typedef long long ll;
const int inf = 1e9;
const int mod = 1e9 + 7;

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

	if (A < 8) {
		cout << -1 << endl;
		return 0;
	}

	int ans = -1;
	rep(i,8,A) {
		int a = A/i;
		if(a==1) {
			int b = A-i;
			if(b==7) {
				ans = i;
				break;
			}
		}
	}
	cout << ans << endl;
	
	return 0;
}