#include<stdio.h>

int main()
{
	freopen("fact.in","r",stdin);
	freopen("fact.out","w",stdout);
	
	int p,n,k,x,i;
	scanf("%d",&p);
	if(p==0) n=1;
    else n=0;        

	do
	{
		i=0;
		k=1;
		x=0;
		while(x-i+1<=p)
		{
			k *= 5;
	        x = 5*x+1;
			i++;
		}
		n += k/5;
		p -= x/5;
	}while(p>0);
	printf("%d\n",n);

	return 0;
}