#include<fstream>
using namespace std;
int main ()
{
	long P,prod,cont=1,s=0,k=5;
	ifstream f("fact.in");
	f>>P;
	if(P==0) prod=1;
	else
	{
		prod=5*P;
		while(k*5<=prod)
		{
			k*=5;
			prod=prod-cont*5;
			cont++;
		}
	}
	ofstream g("fact.out");
	g<<prod;
	f.close();
	g.close();
	return 0;
}