#include <iostream>
#include <fstream>
using namespace std;


int fact(int n){
	int putere = 0;
	while (n % 5 == 0){
		putere++;
		n = n / 5;
	}
	return putere;
}

int main() {
	ifstream in;
	ofstream out;
	in.open("fact.in");
	out.open("fact.out");
	int p, n;
	in >> p;
	n = 1;
	int nr_cifre = 0;
	if (nr_cifre == p){
		cout << n - 1;
		return 0;
	}
	while (nr_cifre != p) {
		nr_cifre += fact(n);
		if (nr_cifre == p){
			out << n ;
			return 0;
		}
		if(nr_cifre > p){
			out << -1;
			return 0;
		}
		n++;
	}
}