Given a string s and an integer k, find the maximum number of vowels that appear together in any contiguous substring of length exactly k.

The vowels are a, e, i, o, u (and only lowercase English letters).

<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 400 60" width="400" height="60"> <rect width="400" height="60" fill="#f8f9fa" rx="4"/> <text x="10" y="38" font-family="monospace" font-size="20" fill="#333">a b c</text> <text x="78" y="38" font-family="monospace" font-size="20" fill="#e63946" font-weight="bold">i i i</text> <text x="150" y="38" font-family="monospace" font-size="20" fill="#333">d e f</text> <text x="10" y="55" font-family="monospace" font-size="11" fill="#888">s = "abciiidef", k = 3</text> </svg>