Given a non-empty array of integers, every element appears two times except for one, which appears exactly once. Find that single one, ine linear time, with no extra memory.
The first line of the input file contains one integer \(N\) the size of the array A. The next line contains \(N\) space separated integers \(a_i\) (\(1 \leq a_i \leq 10^5\)).
Output one line with one integer : the element that occurs exactly once.
7 2 2 3 3 4 4 1