arr = input().split()
h=int(arr[0])
w=int(arr[1])

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