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

	read(*,*) h,w

	b = 0

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