Given a string s representing a license key and an integer k, reformat s so that the groups of characters are separated by dashes and each group contains exactly k characters, except possibly the first group, which may contain fewer than k characters.

The reformatted string should use uppercase letters only. Remove all existing dashes from s before grouping the characters.

Return the reformatted license key.

Constraints:

• $1 \leq$ s.length $\leq 10^5$

• s consists of English letters, digits, and dashes '-'.

• $1 \leq$ k $\leq 10^4$

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