function sum (id, pr, n, a):
    lo := id * n / pr
    hi := (id + 1) * n / pr

    s := 0
    for i := lo until hi:
        s ^= a[i]
    send (0, s)

    if id == 0:
        r := 0
        for k := 0 until pr:
            r ^= receive (k)
        print (r)