module module1
  sub main()
    dim str as string
    str = console.readline()
    dim a as string()
    a = split(str)
    dim b as string
    if a(0)>=a(1)*2 then
      b = a(0)-a(1)*2
      console.writeline(b)
    else
      console.writeline(0)
    end if
  end sub
end module