a, b, c = list(map(int, input().split()))

print((int(a*b/2)))
a, b, c = list(map(int, input().split()))

ans = a * b // 2

print(ans)

a, b, c = list(map(int, input().split()))
print((int(a * b / 2)))

a, b, c = list(map(int, input().split()))
ans = a * b // 2
print(ans)

-print((int(a * b / 2))) +ans = a * b // 2 +print(ans)