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

long long tot,cinci,p,i;

int main()
{
freopen("fact.in","r",stdin);
freopen("fact.out","w",stdout);
scanf("%lld",&p);
i=1;
while(cinci<p)
  {
  i++;
  while(cinci%5==0)
    tot++;
  }
printf("%lld",tot);
}