#include <stdio.h>
#include <stdlib.h>
#include <iostream>
#include <fstream>
using namespace std;
int main(){
    int p,i=1,S=0,b;
    ifstream in("fact.in");
    ofstream out("fact.out");
    in>>p;
    while(p!=S){
           b=i;

          while(b%5==0){

          b=b/5;
          S=S+1;
          if(p==S) break;

        }


        i++;


    }

out<<S<<"\n";
in.close();
    out.close();
return 0;




}