During a stress test, every sensor ID logs twice except ONE faulty sensor that logs only once — Nusrat must find it using O(1) extra memory, no arrays allowed. Read N integers where every value appears EXACTLY TWICE except one value which appears exactly once. Find that value in O(N) time and O(1) extra space using XOR (do not use a hashmap/array counting approach).
Input
First line N (odd), second line N integers.
Output
The single non-duplicate value.
Constraints
1 ≤ N ≤ 2×10^5, N is odd
Sample Input
5 4 1 2 1 2
Sample Output
4
main.c
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