using System;

public class Program

{

    public static void Main()

    {

        int ans, circlerad, length, width, choice;

        Console.Write("Input 1 for area of Circle \nInput 2 for area of Rectangle \nInput 3 for area of Triangle \nPlease Input your choice : ");

        choice = byte.Parse(Console.ReadLine());

        switch (choice)

        {

            case '1' :

                Console.Write("Please enter radius of circle : ");

                circlerad = int.Parse(Console.ReadLine());

                ans = 21 * (circlerad * circlerad);

                Console.Write("The area is : {0}",ans);

                break;

            case '2' :

                Console.Write("Please enter length of rectangle : ");

                length = int.Parse(Console.ReadLine());

                Console.Write("Please enter width of rectangle : ");

                width = int.Parse(Console.ReadLine());

                ans = (length * width);

                Console.Write("The area is : {0}",ans);

                break;

            case '3' :

                Console.Write("Please enter length of triangle : ");

                length = int.Parse(Console.ReadLine());

                Console.Write("Please enter width of triangle : ");

                width = int.Parse(Console.ReadLine());

                ans = (length * width)/2;

                Console.Write("The area is : {0}",ans);

                break;

            default:

                Console.Write("ERROR");

                break;

        }

    }

}