#include<iostream>
#include<fstream>
using namespace std;
int doi = 0, cinci = 0;

ifstream f("fact.in");
ofstream g("fact.out");

void next(int c){ int aux = c;
  while (!(aux % 2)) {doi++; aux = aux/2;}
  aux = c;
  while (!(aux % 5)) {cinci++; aux = aux/5;}
}

int main(){
  int p, c = 2;
  f >> p;
    while (doi < p || cinci < p)
     next(c++);
  g << c-1;
return 0;
}