datas = input().split(" ")

h = int(datas[0])
w = int(datas[1])


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