#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;

#define rep(i, n) REP(i, 0, n)
#define ALL(v) v.begin(), v.end()
#define MSG(a) cout << #a << " " << a << endl;
#define REP(i, x, n) for (int i = x; i < n; i++)
#define OP(m) cout << m << endl
typedef long long ll;
typedef unsigned long long ull;

int main()
{
    int n;
    while (cin >> n, n)
    {
        int cnt = 0;
        for (int i = 1; i <= n; i++)
        {
            int m = i;
            while (m % 5 == 0)
            {
                cnt++;
                m /= 5;
            }
        }
        OP(cnt);
    }
    return 0;
}
