calculate circle foruma for area with input value, c#

ConsoleApp.BasicCSharp

using System;

namespace ConsoleApp.BasicCSharp
{
    class ExecuteProgram
    {
        static void Main(string[] args)
        {
            Circle circle = new Circle();

            circle.PrintResult();
        }
    }

    class Circle
    {
        double radius;
        double pi = Math.PI;

        public void Input()
        {
            Console.Write("Input Value r = ");
            radius = double.Parse(Console.ReadLine());

            Console.WriteLine($"Value pi = {pi}");
        }

        public double Calculate()
        {
            Console.WriteLine("\nFormula : pi * r * r");

            return pi * radius * radius;
        }

        public void PrintResult()
        {
            Console.WriteLine("===============================");    
            Console.WriteLine("   Circle Formula for Area");    
            Console.WriteLine("===============================");    

            Input();
            var result = Calculate();

            Console.WriteLine($"\nResult : {result}");
        }
    }
}