# include <iostream>
# include <fstream>

std::ifstream cin ("factorial.in");
std::ofstream cout ("factorial.out");

int p;

/* numarul de zerouri continute de n! */
int number_zero (int n) {
	int p = 5, res = 0;
	while (p <= n) {
		res = res + n / p;
		p = p * 5;
	}
	return res;
}
int cautare (int ls, int ld) {
	while (ls <= ld) {
		int m = ls - (ls - ld) / 2;
		if (number_zero (m) < p)
			ls = m + 1;
		else 
			ld = m - 1;
	}
	if (number_zero (ls) == p)
		return ls;
	return -1;
}
int main (void) {
	cin >> p;
	cout << cautare (1, 5 * p);
	return 0;
}