program abc
	implicit none
	integer :: i,j,b
    integer(16) :: h,w,a

	read(*,*) h,w

	a = h * w
    
    if(mod(a,2) /= 0) then
    	a = (h * w + 1) / 2
    else
    	a = h * w / 2
    endif
	
	write(*,*) a
    
end program abc