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

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

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

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

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