You are given an integer array `values` where values[i] represents the value of the `ith` sightseeing spot. Two sightseeing spots `i` and `j` have a distance `j - i` between them.

The score of a pair (`i < j`) of sightseeing spots is `values[i] + values[j] + i - j`: the sum of the values of the sightseeing spots, minus the distance between them.

Return the maximum score of a pair of sightseeing spots.

Example 1:

    Input: values = [8,1,5,2,6]
    Output: 11
    Explanation: i = 0, j = 2, values[i] + values[j] + i - j = 8 + 5 + 0 - 2 = 11

Example 2:

    Input: values = [1,2]
    Output: 2

Constraints:

- `2 <= values.length <= 5 * 104`
- `1 <= values[i] <= 1000`