The Lonely Number

Difficulty: 1200 3000 ms 128 MB

bitwise

Every value appears exactly twice, except one that appears once. Find it — ideally without extra memory.

Input: the first line has N (odd); the second line has N positive integers.

Output: the value that appears once.

Constraints:

• 1 ≤ N ≤ 10⁵
• 1 ≤ a_i ≤ 10⁶

Sample Tests

5
2 3 5 3 2

5

1
42

42

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