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