You are given the string `croakOfFrogs`, which represents a combination of the string `"croak"` from different frogs, that is, multiple frogs can croak at the same time, so multiple `"croak"` are mixed.

Return the minimum number of different frogs to finish all the croaks in the given string.

A valid `"croak"` means a frog is printing five letters `'c'`, `'r'`, `'o'`, `'a'`, and `'k'` sequentially. The frogs have to print all five letters to finish a croak. If the given string is not a combination of a valid `"croak"` return `-1`.

Example 1:

    Input: croakOfFrogs = "croakcroak"
    Output: 1
    Explanation: One frog yelling "croak" twice.

Example 2:

    Input: croakOfFrogs = "crcoakroak"
    Output: 2
    Explanation: The minimum number of frogs is two.
    The first frog could yell "crcoakroak".
    The second frog could yell later "crcoakroak".

Example 3:

    Input: croakOfFrogs = "croakcrook"
    Output: -1
    Explanation: The given string is an invalid combination of "croak" from different frogs.

Constraints:

- `1 <= croakOfFrogs.length <= 105`
- `croakOfFrogs` is either `'c'`, `'r'`, `'o'`, `'a'`, or `'k'`.