n,k = map(int,input().split())
s = (input())
def longestSubString(start, end, s, k):

    count = [0 for i in range(26)]

    for i in range(start, end):
        count[ord(s[i]) - ord('a')] += 1

    for i in range(start, end):
        if (count[ord(s[i]) - ord('a')] < k):

            left = longestSubString(start, i,
                                    s, k)

            right = longestSubString(i + 1, end,
                                     s, k)
            return max(left, right)

    return end - start
print(longestSubString(0,n,s,k))