#include <iostream>
#include <fstream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int n,cinci=25,nr,x=1,p;
int main ()
{
	f>>p;
	if (p)
	{
	nr=p*5;
	while (cinci<nr)
	{
		while (x*cinci<nr)
		{
			nr-=5;
			x++;
		}
		x=1;
		cinci*=5;
	}
	g<<nr;
	return 0;
	}
	else
		g<<"1";
}