def longest_k_distinct(text, k):
    if k <= 0:
        return 0
    counts = {}
    left = best = 0
    for right, char in enumerate(text):
        counts[char] = counts.get(char, 0) + 1
        while len(counts) > k:
            old = text[left]
            counts[old] -= 1
            if counts[old] == 0:
                del counts[old]
            left += 1
        best = max(best, right - left + 1)
    return best