How to take user input and calculate rectangle area in C#

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

namespace Practice

{

    class ConvertAndSize

    {

        public void takeinout()

        {

            const double pi = 3.14;

            double r;

            Console.WriteLine("ENTER RADIUS : ");

            r = Convert.ToDouble(Console.ReadLine());

            double area = pi * r * r;

            Console.WriteLine("Area is {0}",area);

            Console.ReadLine();

        }

        }
}

class Program

    {

        static void Main(string[] args)

        {

            ConvertAndSize c = new ConvertAndSize();

            c.takeinout();

        }
    }

Output :

Enter radious :

10

Area is 314