#include <bits/stdc++.h>

using namespace std;

typedef long long int big;

int main(){
    big n;
    while(cin>>n){
    big div=5;
    big count=0;
    while(n/div!=0){
        count+=n/div;
        div=div*5;
    }
    cout<<count<<endl;}
    return 0;
}