h,w=map(int,input().split())
if h==1 or w==1:
    print(1)
    exit()
if h%2+w%2==0:
    print((h//2)*w)
elif h%2==1 and w%2==0:
    print((w//2)*h)
elif w%2==1 and h%2==0:
    print((h//2)*w)
else:
    print((h//2+1)*(w-w//2)+(h//2)*(w//2))
