#include "bits/stdc++.h"
using namespace std;
#define LL long long
#define INF 0x3f3f3f3f3f
#define PI acos(-1)
#define N 510
LL arr[N];
int main()
{
    int n,k;
    while(~scanf("%d",&n)){
        int sum=0;
        while(n>0){
            sum
 
+=n/5;
            n/=5;
        }
        printf("%d\n",sum);
    }
    return 0;
}

51Nod 1003 階乘後面0的數量 | 思維