#include<iostream>
#include<fstream>
using namespace std;

ifstream fin("fact.in");
ofstream fout("fact.out");

int main(){
    int n,i,k=0,x,p;
    fin>>n;
    p=5;k=0;
    while(p<=n){k=k+n/p;
                p=p*5;}
    fout<<k;
    return 0;
}