CF676C Vasya and String

High school student Vasya got a string of length $ n $ as a birthday present. This string consists of letters 'a' and 'b' only. Vasya denotes beauty of the string as the maximum length of a substring (consecutive subsequence) consisting of equal letters. Vasya can change no more than $ k $ characters of the original string. What is the maximum beauty of the string he can achieve?

The first line of the input contains two integers $ n $ and $ k $ ( $ 1

Print the only integer — the maximum beauty of the string Vasya can achieve by changing no more than $ k $ characters.

In the first sample, Vasya can obtain both strings "aaaa" and "bbbb". In the second sample, the optimal answer is obtained with the string "aaaaabaa" or with the string "aabaaaaa".