https://www.e-olymp.com/az/problems/123

/*
    Author: Kanan Asgarli
    https://www.e-olymp.com/az/problems/123
*/
#include <iostream>
#include <algorithm>
using namespace std;
int n, sum;
int main()
{
    cin>>n;
    while(n > 0){
        n = n/5;
        sum += n;
    }
    cout<<sum<<endl;
    return 0;
}