#include <bits/stdc++.h>  

using namespace std;

#define FOR(i, j, k) for(int i = j; i < k; ++i)
#define rep(i, j) FOR(i, 0, j)
#define repr(i, j) for(int i = j; i >= 0; --i)
#define INF (1 << 30)
#define MOD 1e9 + 7

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> P;


int main() {
	int N;
	while(scanf("%d", &N), N) {
		int keta = (int)log10((double)N) + 1;
		int cnt = 1;
		int ans = 0;
		while(cnt <= keta) {
			int tmp = pow(5, cnt);
			++cnt;
			ans += N / tmp;
		}
		printf("%d\n", ans);
	}
	return 0;
}