h, w = map(int, input().split())
hei = int(h / 2) if h % 2 == 0 else (int(h / 2) + 1)
wid = int(h / 2) if h % 2 == 0 else int((h - 1) / 2)
res = int(w / 2) * (hei + wid) if w % 2 == 0 else (int(w / 2) * (hei + wid)) + hei
print(res)
