#include<stdio.h>

int main(void)
{
	unsigned long long int kai=1;
	int n,i,x=0;
	while(scanf("%d",&n)!=0)
	{
		for(i=1;i<n+1;i++)
		{
			 kai=kai*i;

			 while(kai % 10 ==0)
			 {
				 kai = kai / 10;
				 x+=1;
			 }
		}
		  printf("%d\n",x);
	}
  return 0;
}