#include<iostream>
#include<sstream>
#include<iomanip>
#include<stdio.h>
#include<math.h>
#include<string>
#include<string.h>
using namespace std;
int main(){
	long long n,sum=0;
	cin>>n;
	while(n!=0){
		sum+=n/5;
		n/=5;
	}
	cout<<sum;
	return 0;
}