#include <iostream>
#include <vector>
#include <list>
#include <algorithm>
#include <string>
#include <stack>
#include <iomanip>
#include <numeric>
#include <queue>
#include <climits>
#include <complex>
#include <cmath>
#include <map>
using namespace std;
using ll = long long;
#define MOD 1000000007
#define INF 1LL << 59

int main()
{
    std::ios::sync_with_stdio(false);
    std::cin.tie(0);
    //cout << fixed << setprecision(3);

    int n;
    while (cin >> n)
    {
        if (n == 0)
            break;
        int cnt = 0;
        for (int i = 1; i <= n; ++i)
        {
            int t = i;
            while (t % 5 == 0)
            {
                t /= 5;
                cnt++;
            }
        }
        cout << cnt << endl;
    }
    return 0;
}
