function problem_b(id, pr, n, a):
    i := id
    s := 0

    while i < n:
        s ^= a[i]
        i += pr

    left := 2 * id + 1
    right := left + 1

    if left < pr:
        s ^= receive(left)
    if right < pr:
        s ^= receive(right)

    if id != 0:
        send((id - 1) / 2, s)
    else:
        print(s)