A string `s` is called good if there are no two different characters in `s` that have the same frequency.

Given a string `s`, return the minimum number of characters you need to delete to make `s` good.

The frequency of a character in a string is the number of times it appears in the string. For example, in the string `"aab"`, the frequency of `'a'` is `2`, while the frequency of `'b'` is `1`.

Example 1:

    Input: s = "aab"
    Output: 0
    Explanation: s is already good.

Example 2:

    Input: s = "aaabbbcc"
    Output: 2
    Explanation: You can delete two 'b's resulting in the good string "aaabcc".
    Another way it to delete one 'b' and one 'c' resulting in the good string "aaabbc".

Example 3:

    Input: s = "ceabaacb"
    Output: 2
    Explanation: You can delete both 'c's resulting in the good string "eabaab".
    Note that we only care about characters that are still in the string at the end (i.e. frequency of 0 is ignored).

Constraints:

- `1 <= s.length <= 105`
- `s` contains only lowercase English letters.