h, w = map(int, input().split())

if h % 2 == 0:
    ans = h / 2 * w
elif w % 2 == 0:
    ans = (h - 1) / 2 * w / 2 + (h + 1) / 2 * w / 2
else:
    ans = (h - 1) / 2 * (w - 1) / 2 + (h + 1) / 2 * (w + 1) / 2

if h == 1 or w == 1:
    ans = 1

print(int(ans))
