#include<stdio.h>
#include<math.h>

int main(){
	int p,k,p1;
	long n;
	freopen("fact.in", "r", stdin);
	freopen("fact.out", "w", stdout);
	scanf("%d",&p);
	
	n=p*5;
	k=0;
	p1=5;
	if(p==0){
		printf("1");
		return 0;
		}
	while(p1<=n){
		p1=p1*5;
		if(p1<=n)		
			k++;
		//printf("%d %d\n",p1,k);
		}
	//printf("%d %d",p,n);
	if(k!=0)
		printf("%d",n-(k*5));
	else
		printf("%d",n);
	return 0;
	}