H, W = [int(i) for i in input().split()]

if H==1 or W==1:
    print(1)
    quit()
if H%2==0:
    H //= 2
    print(H*W)
elif W%2==0:
    W //= 2
    print(H*W)
else:
    W -= 1
    c = (W//2)*H
    c += H//2 + 1
    print(c)
