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

namespace AtCoder
{
  class Program
  {
    static void Main(string[] args)
    {
      int input = int.Parse(Console.ReadLine());
      
      double result = input * input * 6.28318530717958623200;
      
      Console.WriteLine(result);
    }
  }
}