#include <bits/stdc++.h>

using namespace std;
ifstream in ("fact.in");
ofstream out ("fact.out");

int main()
{
    int n, crtNum = 0;
    in >> n;
    for(long long i=5; i<= n; i*=5){
      crtNum+= n/i;
    }
    out << crtNum;
    return 0;
}