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


            b=i;
        while(i%2==0){
          k++;
          b=b/2;
        }
        while(i%5==0){
          a++;
          b=b/5;
        }
        if(k<a) {S=S+k;
                 k=0;
                 a=a-k;
        }
              else {S=S+a;
                     a=0;
                     k=a-k;
              }

        i++;


    }

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




}