You are given a license key represented as a string `s` that consists of only alphanumeric characters and dashes. The string is separated into `n + 1` groups by `n` dashes. You are also given an integer `k`.

We want to reformat the string `s` such that each group contains exactly `k` characters, except for the first group, which could be shorter than `k` but still must contain at least one character. Furthermore, there must be a dash inserted between two groups, and you should convert all lowercase letters to uppercase.

Return the reformatted license key.

Example 1:

    Input: s = "5F3Z-2e-9-w", k = 4
    Output: "5F3Z-2E9W"
    Explanation: The string s has been split into two parts, each part has 4 characters.
    Note that the two extra dashes are not needed and can be removed.

Example 2:

    Input: s = "2-5g-3-J", k = 2
    Output: "2-5G-3J"
    Explanation: The string s has been split into three parts, each part has 2 characters except the first part as it could be shorter as mentioned above.

Constraints:

- `1 <= s.length <= 105`
- `s` consists of English letters, digits, and dashes `'-'`.
- `1 <= k <= 104`