//  Trailing Zeros

#include<bits/stdc++.h>

using namespace std;
using ll = long long;

int main() {
    int count = 0;
    ll n; cin >> n;
    for (int i = 1; i <= 15; i++) {
        count += n / pow(5, i);
    }
    cout << count;
    return 0;
}