#include<stdio.h>
long long k,n,i,aux,nr;
int main ()
{
	freopen("fact.in","r",stdin);
	freopen("fact.out","w",stdout);
	scanf("%lld",&n);
	for(i=5;i<=n;i+=5)
	{
		aux=i;
		nr=0;
		while(aux%5==0)
		{
			aux/=5;
			nr++;
		}
		n-=nr;
	}
	k=n*5;
	printf("%lld",k);
	return 0;
}