------
## 最终结论
```python
def search(arr, n):
    for i in range(n):
        if (i == 0 and arr[i] != arr[i + 1]) or (i == n - 1 and arr[i] != arr[i - 1]) or (0 < i < n - 1 and arr[i] != arr[i - 1] and arr[i] != arr[i + 1]):
            return arr[i]

# Test cases
assert search([1,1,2,2,3],5) == 3
assert search([1,1,3,3,4,4,5,5,7,7,8],11) == 8
assert search([1,2,2,3,3,4,4],7) == 1
```