using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
 
namespace ConsoleApplication13
{
    class Program
    {
        static void Main(string[] args)
        {
            string input = Console.ReadLine();
 
            int bufor = 0;
            double d = 0.0, r = 0.0;
            double result=0.0;
 
            for (int i = 0; i < input.Length; i++)
            {
                if (input[i] == ' ')
                {
                    bufor = i + 1;
 
                    r = double.Parse(input.Substring(0, bufor).Replace('.', ','));
                    break;   
                }
 
            }
            d = double.Parse(input.Substring(bufor, input.Length - bufor).Replace('.', ','));
 
            result = (((r*r)-((d*d)*0.25))* 3.141592654);
 
            Console.WriteLine(Math.Round(result,2).ToString().Replace(',','.'));
        }
    }
}
 

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