#include<stdio.h>
long long k,n,i,aux,nr,a,a2,nn,n2,av,aw,n1,init;
int main ()
{
	freopen("fact.in","r",stdin);
	freopen("fact.out","w",stdout);
	scanf("%lld",&n);
	if(n==0)
		printf("0");
	nn=n;
	init=n;
	long long ann=1,nn1;
	long long an2=1;
	for(i=1;i<=11;i++)
	if(nn>=5)
	{
		n=init;
		nn/=5;
		nn1=nn;
		ann*=nn;
		n-=ann;
		nn=n;
		nn/=5;
		an2*=(nn1-nn);
		n+=an2;
	}
	else
		break;
	
	printf("%lld",5*n);
}