Polo the Penguin and the XOR

Read problems statements in Russian here Polo, the Penguin, likes the XOR operation. Please read NOTE if you are not familiar with XOR operation. XOR-sum of a list of numbers is the result of XOR-ing all of them. XOR-sum of (A[1] XOR A[2] XOR ... XOR A[N]) is defined as A[1] XOR (A[2] XOR (A[3] XOR ( ... XOR A[N]))). He has an array A consisting of N integers. Index in the array are numbered fr