You are given an integer array `nums` with the following properties:

- `nums.length == 2 * n`.
- `nums` contains `n + 1` unique elements.
- Exactly one element of `nums` is repeated `n` times.

Return the element that is repeated `n` times.

Example 1:

    Input: nums = [1,2,3,3]
    Output: 3

Example 2:

    Input: nums = [2,1,2,5,3,2]
    Output: 2

Example 3:

    Input: nums = [5,1,5,2,5,3,5,4]
    Output: 5

Constraints:

- `2 <= n <= 5000`
- `nums.length == 2 * n`
- `0 <= nums[i] <= 104`
- `nums` contains `n + 1` unique elements and one of them is repeated exactly `n` times.