A sensor logs integer readings into a buffer. By design, every distinct reading value is recorded an even number of times — except for exactly one "lonely" value that was recorded an odd number of times. Given the buffer, recover that lonely value.
The input guarantees that exactly one value has an odd count, so the answer is unique.
Input format
Line 1: an integer n, the number of readings.
Line 2: n space-separated non-negative integers, the readings.
Output format
A single integer: the value whose count in the buffer is odd.
Constraints
- 1 ≤ n ≤ 100000
- 0 ≤ each reading ≤ 1000000000
- Exactly one value occurs an odd number of times; all others occur an even number of times.