#include<iostream>
#include<algorithm>
using namespace std;

int main(){
	int n;
	while(cin>>n){
		int cnt2 = 0, cnt5 = 0, temp = 2;
		while(temp <= n){
			cnt2 += n/temp;
			temp *= 2;
		}
		temp = 5;
		while(temp <= n){
			cnt5 += n/temp;
			temp *= 5;
		}
		cout<<min(cnt2, cnt5)<<endl;
	}
}