HW5.36

 import java.util.Scanner;

 public class Solution
 {
     public static void main(String[] args)
     {
         Scanner input = new Scanner(System.in);
         System.out.print("Enter the number of sides: ");
         int n = input.nextInt();
         System.out.print("Enter the length of sides: ");
         double sides =input.nextDouble();

         input.close();

         System.out.println(area(n, sides));
     }

     public static double area(int n, double side)
     { return n * side * side / (4 * Math.tan(Math.PI / n)); }
 }