201571: [AtCoder]ARC157 B - XYYYX

Problem Statement

You are given a string $S$ of length $N$ consisting of X and Y. You will choose $K$ characters at distinct positions in $S$ and change each of them: X becomes Y and Y becomes X. Find the maximum possible number of pairs of consecutive Ys in the resulting string.

Constraints

• $1 \leq N \leq 2 \times 10^5$
• $0 \leq K \leq N$
• $S$ is a string of length $N$ consisting of X and Y.

Input

The input is given from Standard Input in the following format:

$N$ $K$
$S$

Output

Print the maximum possible number of pairs of consecutive Ys in the resulting string.

Sample Input 1

5 1
XYXYX

Sample Output 1

2

You will choose one character.

• If you choose the $1$-st character, the resulting string is YYXYX, with one pair of consecutive Ys at positions $1, 2$.
• If you choose the $2$-nd character, the resulting string is XXXYX, with no pair of consecutive Ys.
• If you choose the $3$-rd character, the resulting string is XYYYX, with two pairs of consecutive Ys at positions $2, 3$ and $3, 4$.
• If you choose the $4$-th character, the resulting string is XYXXX, with no pair of consecutive Ys.
• If you choose the $5$-th character, the resulting string is XYXYY, with one pair of consecutive Ys at positions $4, 5$.

Thus, the sought maximum number is $2$.

Sample Input 2

5 4
XYXYX

Sample Output 2

2

It is optimal to choose the $1$-st, $2$-nd, $3$-rd, and $5$-th characters to get YXYYY, or choose the $1$-st, $3$-rd, $4$-th, and $5$-th characters to get YYYXY. Note that you may not choose a character at the same position multiple times.