using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            double r=0;
            Circle a = new Circle();
            Console.WriteLine("請輸入圓形半徑");
            r=int.Parse(Console.ReadLine());
            a.SetRadius(r);
            Console.WriteLine("圓形半徑={0}，圓形面積={1}",r, a.GetArea());

        }
    }

    class Circle
    {
        private double radius;
        public void SetRadius(double r)
        {
            radius = r;
        }

        public double GetArea()
        {
            return radius*radius*Math.PI;
        }
    }

}