#include <iostream>
#include <fstream>
#include <string>

using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int nrZerouri(long long int a) {
	int sum = 0;
	while (a != 0) {
		int rest = a % 10;
		if (rest == 0) sum++; else
			break;
		a /= 10;
	}
	return sum;
}
long long int fact(int n) {
	if (n >= 1) { return n * fact(n - 1); }
	else { return 1; }
}

int main()
{
	int a;
	fin>> a;
	int zerouri[1000];
	string s;
	for (int i = 1; i <= 100; i++) {
		if (nrZerouri(fact(i)) == a) {
			fout << i; break;
		}
	}
	fin.close();
	fout.close();
	return 0;
	
}