Bear and Xor of Sums

Limak is a problem setter. Since he is lazy and cunning, he usually takes old problems and modifies them a bit (to not be accused of plagiarism), e.g. by swapping two words in the statement. This is how he created the following problem (and your task is to solve it): Given a sequence with N positive integers, find the xor of sums of all non-empty segments of the sequence. In other words, for e