#include<iostream>
#include<fstream>
using namespace std;
int main()
{
	int nr,p,n,aux,i;
	ifstream f("fact.in");
	ofstream g("fact.out");
	f>>p;
	n=0;
	for(i=1;i<=p;i++)
	{	nr=-1;
		n=n+5;
		aux=n;
		while(aux!=0)
		{	if(aux%5==0)
				nr++;
			else
				aux=0;
			aux=aux/5;
		}
		i=i+nr;
	}
	g<<n;
	f.close();
	g.close();
	return 0;
}