def solution(start, length):
    checksum = 0
    for i in range(length):
        base = start + length * i
        for j in range(length - i):
            checksum ^= base + j
    return checksum

tests = [
        ([0, 3], 2),
        ([17, 4], 14)
        ]

for i, o in tests:
    result = solution(*i)
    print (i, result == o, result, o)