Taco Tile Challenge

You are given a sequence consisting of tiles, each represented by a character: 'B' for black and 'W' for white. Your task is to determine if there exists a contiguous subsequence of exactly k tiles such that every adjacent pair of tiles in this subsequence are of different colors.

Formally, given a tile sequence S of length n and a positive integer k, find an index i (1 ≤ i ≤ n-k+1) such that for every index j (i ≤ j < i+k-1), the following condition holds:

\( S[j] \neq S[j+1] \)

If k = 1, the answer is always "yes" since a single tile trivially satisfies the condition.

inputFormat

The input is given in two lines:

• The first line contains two integers n and k separated by space, where n is the number of tiles.
• The second line contains a string of length n representing the tile sequence. Each character is either 'B' or 'W'.

outputFormat

Output a single line containing either "yes" if there exists a contiguous subsequence of exactly k alternating tiles, or "no" otherwise.

6 4
BWBWBW

yes