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

if w == 1 or h == 1:
  print(1)
  exit()

res = 0
if h % 2 == 1:
  if w % 2 == 0:
    res = w//2 * (h//2) + w//2 * (h // 2 + 1)
  else:
    res = w//2 * (h//2) + (w//2 +1) * (h // 2 + 1) 
else:
    if w % 2 == 0:
      res = w * (h // 2)
    else:
      res = (w//2) * (h//2) + (w//2 + 1) * (h//2)
  
print(res)