#include<stdio.h>
int k,i,p,aux,y,j;
long n;
long long q;
FILE *f=fopen("fact.in","r"),*g=fopen("fact.out","w");
int main()
{
fscanf(f,"%d",&p);
k=0;y=1;
aux=0;
n=100000;
 for(i=1;i<=n;i++)
{	if(i%5==0)
	{k++;
		q=2*i;}
if((k==p-1)||(k==p))
	while(q!=0)
	{ if(q%10==0)
		j++;
	q=q/10;
}
		
	
 }
 if(p!=0)
 fprintf(g,"%d",j);
else
 fprintf(g,"%d",y);
fclose(f);
fclose(g);
return 0;
}