#include <iostream>
using namespace std;

int main(){
	int a;
	cin >> a;
	for(int i = 2;i < a;i++){
		int tmp = a,digit = 1;
		string s = "";
		while(tmp >= digit * i) digit *= i;
		while(digit){
			s += to_string(tmp / digit);
			tmp %= digit;
			digit /= i;
		}
		if(s == "17"){
			cout << i << endl;
			return 0;
		}
	}
	cout << -1 << endl;
}