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