n, m = map(int, input().split())

if n == 1 or m == 1:
    print((n * m) // 4)
elif n % 2 == 0 and m % 2 == 0:
    print(0)
elif n % 2 == 0 or m % 2 == 0:
    even = n if n % 2 == 0 else m
    print(even // 4)
else:
    print(0)