You are given an array of positive integers `arr`. Perform some operations (possibly none) on `arr` so that it satisfies these conditions:

- The value of the first element in `arr` must be `1`.
- The absolute difference between any 2 adjacent elements must be less than or equal to `1`. In other words, `abs(arr[i] - arr[i - 1]) <= 1` for each `i` where `1 <= i < arr.length` (0-indexed). `abs(x)` is the absolute value of `x`.

There are 2 types of operations that you can perform any number of times:

- Decrease the value of any element of `arr` to a smaller positive integer.
- Rearrange the elements of `arr` to be in any order.

Return the maximum possible value of an element in `arr` after performing the operations to satisfy the conditions.

Example 1:

    Input: arr = [2,2,1,2,1]
    Output: 2
    Explanation:
    We can satisfy the conditions by rearranging arr so it becomes [1,2,2,2,1].
    The largest element in arr is 2.

Example 2:

    Input: arr = [100,1,1000]
    Output: 3
    Explanation:
    One possible way to satisfy the conditions is by doing the following:
    1. Rearrange arr so it becomes [1,100,1000].
    2. Decrease the value of the second element to 2.
    3. Decrease the value of the third element to 3.
    Now arr = [1,2,3], which satisfies the conditions.
    The largest element in arr is 3.

Example 3:

    Input: arr = [1,2,3,4,5]
    Output: 5
    Explanation: The array already satisfies the conditions, and the largest element is 5.

Constraints:

- `1 <= arr.length <= 105`
- `1 <= arr[i] <= 109`