# include <iostream>
# include <cstring>
# include <string>
# include <vector>
# include <cmath>
# include <sstream>
# include <iomanip>
# include <algorithm>
using namespace std;

# define repl(i, a, b)	for(int i=(int)(a);i<(int)(b);i++)
# define rep(i, n)	repl(i, 0, n)
typedef long long ll;

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

	if(A == 17){
		cout << 10 << endl;
		return 0;
	}
	for(int i=1;i<A;i++){
		if(A / i == 1 && A % i == 7){
			cout << i << endl;
			return 0;
		}
	}
	cout << -1 << endl;
	return 0;
}