w, h = map(int, input().split())
if w % 2 == 0:
two_1_cnt = w // 2
three_cnt = 0
else:
two_1_cnt = (w - 3) // 2
three_cnt = 1
three_2_cnt = 1 # 2nd row
w2 = w - 3
if w2 % 2 == 1:
three_2_cnt += 1
ans = (h // 2) * (three_cnt + three_2_cnt)
if h % 2:
ans += three_cnt
print(ans)