!!!**********************************************************************
program main
!!!**********************************************************************  

  integer   :: n, d, x
  ! real      ::
  ! character ::
  
!!!----------------------------------------------------------------------

  read ( unit = *, fmt = * ) n, d

  x = nint(real(n)/real(2*d+1))

  if ( mod(n,2*d+1) /= 0 ) then

     x = x + 1

  end if
  
  print "(i0)", x  
  
!!!**********************************************************************  
end program main
!!!**********************************************************************
