h, w = map(int, input().split())
if h == 1 or w == 1:
  print(1)
else:
  if w % 2 == 0:
      a = (w//2) * 2
      if h % 2 == 0:
          count = a * (h//2)
      else:
          count = a * (h//2)
          count += a // 2
  else:
      a = (w//2) * 2 + 1
      if h % 2 == 0:
          count = a * (h//2)
      else:
          count = a * (h//2)
          count += a//2+1

  print(count)