H,W = map(int,input().split())
 
if (H == 1)or(W == 1):
    sum = 1
elif H % 2 == 0:
    sum = W * H / 2
elif W % 2 == 0:
    sum = (W * (H-1) / 2) + (W / 2)
else:
    sum = (W * (H-1) / 2) + ((W+1) / 2)
 
print(int(sum))