学步园

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

namespace ConsoleApplication2
{
    class Program
    {
        static void Main(string[] args)
        {
           
            const double PI = 3.1415926;
            Console.WriteLine("请输入半径");
            double r, s;
            r = double.Parse(Console.ReadLine());
            s = PI * r * r;
            Console.WriteLine("{0:f}",s);
            Console.ReadLine();
        }
    }
}