program main
  implicit none
  integer*8 :: h, w, ans
  read *, h, w
  if (mod(h, 2) == 0 .or. mod(w, 2) == 0) then
    ans = h * w / 2 
  else
    ans = (h * w + 1)/ 2
  end if
  print '(i0)', ans
end program