program main
  implicit none
  integer(8) :: H,W,out
  integer(8) :: a,b, i,j

  read(*,*) H,W
  if (H == 1 .or. W == 1) then
     write(*,'(i0)') 0
     stop
  end if
  if (mod(W,2) == 0) then
     a = W/2
     b = W/2
  else
     a = W/2 + 1
     b = W/2
  end if
  out = 0
  if ( mod(H,2) == 0 ) then
     out = H/2*a + H/2*b
  else
     out = (H/2+1)*a + H/2*b
  end if
  write(*,'(i0)') out 
end program main
