Pls help me to find Task and Solutions for Russian olympiad of informatic 2009 !!!

http://www.spoj.com/problems/HWAYADS/en/

The sequence of non-negative integers A1, A2, ..., AN is given. You are to find some subsequence Ai1, Ai2, ..., Aik (1 <= i1 < i2 < ... < ik <= N) such, that Ai1 XOR Ai2 XOR ... XOR Aik has a maximum value.

Input The first line of the input file contains the integer number N (1 <= N <= 100). The second line contains the sequence A1, A2, ..., AN (0 <= Ai <= 10^18).

Output Write to the output file a single integer number -- the maximum possible value of Ai1 XOR Ai2 XOR ... XOR Aik.

Given a non directed graph G = (V,E) and K query, N vertices and M arcs. (N,M,K <= 100000) for i-th query, I have 2 number (u[i],v[i]), it mean, if arcs(u[i],v[i]) don't exist, I will add them. if arcs(u[i],v[i]) exist, I will delete them. In M arcs, I have N-1 arcs can't be delete, it's spanning tree. So for each i-th query, I must find the number of bridges on this graph. Pls give me some idea for this problems. thank!!!

P/s : sorry for my bad english