Imports System.Collections
Imports System.Collections.Generic
Imports System.Linq
Imports System.xml
Imports System.xml.Linq

Module Module1
  const PI as double  = 3.1415926535897931
	public sub main()

		dim N as string = Console.ReadLine()
		dim num as integer = convert.toint32(N)
		dim result as double = num * 2.0 * PI

		console.writeLine(result.tostring())
	  
	end sub 
End Module