//============================================================================
// Name        : Factotial.cpp
// Author      : AndreiFlorescu
#include <iostream>
#include <fstream>
#include <math.h>
using namespace std;

int main()
{
	unsigned long int p,f=1, n = 1;
	ifstream file_in("fact.in");
	ofstream file_out("fact.out");
	file_in >> p;
	do
	{
		f = f*n++;
		if(f%10 == 0)
		{
			f /= 10;
			p--;
		}
	}while(p > 0);
	file_out << n-1;
	return 0;
}