#include <vector>
#include <list>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <algorithm>
#include <sstream>
#include <iostream>
#include <string>
#include <cstdio>
#include <cmath>

using namespace std;

int main() {

	int A;
	cin >> A;

	int x = 8;
	while (1) {
		if (A <= 8 || x==100) break;
		int t = A;
		if (t / x * 10 + t%x == 17) {
			cout << x << endl;
			return 0;
		}
		x++;
	}

	cout << -1 << endl;

	return 0;
}