l01ex24.java

import java.util.Scanner;

class Main {

  public static void main(String[] args) {
    int n, i;
    double prod = 1;
    Scanner leitor = new Scanner(System.in);
    
    n = leitor.nextInt();
    
    for (i=1; i<=n; i++) {
      prod *= (4.0*i*i)/(4.0*i*i - 1.0);
    }
    System.out.println(2*prod);
    
  }
}