n, m = map(int, input().split())
s = n * m
r = s % 4

if n == 1 or m == 1:
    print((s - r) // 4)
else:
    if r == 0 or r == 2:
        print(0)
    else:
        if (n % 2 == 1) and (m % 2 == 1):
            print(0)
        else:
            print(1)