You are given an array of unique integers `salary` where `salary[i]` is the salary of the `ith` employee.

Return the average salary of employees excluding the minimum and maximum salary. Answers within `10-5` of the actual answer will be accepted.

Example 1:

    Input: salary = [4000,3000,1000,2000]
    Output: 2500.00000
    Explanation: Minimum salary and maximum salary are 1000 and 4000 respectively.
    Average salary excluding minimum and maximum salary is (2000+3000) / 2 = 2500

Example 2:

    Input: salary = [1000,2000,3000]
    Output: 2000.00000
    Explanation: Minimum salary and maximum salary are 1000 and 3000 respectively.
    Average salary excluding minimum and maximum salary is (2000) / 1 = 2000

Constraints:

- `3 <= salary.length <= 100`
- `1000 <= salary[i] <= 106`
- All the integers of `salary` are unique.