Problem:
Score : 400 points

Problem Statement

There are N people standing in a queue from west to east.

Given is a string S of length N representing the directions of the people.
The i-th person from the west is facing west if the i-th character of S is L, and east if that character of S is R.

A person is happy if the person in front of him/her is facing the same direction.
If no person is standing in front of a person, however, he/she is not happy.

You can perform the following operation any number of times between 0 and K (inclusive):

Operation: Choose integers l and r such that 1 \leq l \leq r \leq N, and rotate by 180 degrees the part of the queue: the l-th, (l+1)-th, ..., r-th persons. That is, for each i = 0, 1, ..., r-l, the (l + i)-th person from the west will stand the (r - i)-th from the west after the operation, facing east if he/she is facing west now, and vice versa.

What is the maximum possible number of happy people you can have?

Constraints

N is an integer satisfying 1 \leq N \leq 10^5.

K is an integer satisfying 1 \leq K \leq 10^5.

|S| = N

Each character of S is L or R.

Input

Input is given from Standard Input in the following format:

N K
S

Output

Print the maximum possible number of happy people after at most K operations.

Sample Input 1

6 1
LRLRRL

Sample Output 1

3

If we choose (l, r) = (2, 5), we have LLLRLL, where the 2-nd, 3-rd, and 6-th persons from the west are happy.

Sample Input 2

13 3
LRRLRLRRLRLLR

Sample Output 2

9

Sample Input 3

10 1
LLLLLRRRRR

Sample Output 3

9

Sample Input 4

9 2
RRRLRLRLL

Sample Output 4

7

Solution in Go (1.6) (judge verdict: Wrong Answer)

package main

import (
	"fmt"
	"unicode/utf8"
)

func main() {
	var a, b int
	var c string
	fmt.Scan(&a, &b, &c)

	seat := spritString(c)
	ans := 0
	if a == 1 {
		ans = 0
	} else if a == 2 {
		if b > 0 {
			ans = 1
		}
	} else {
		changeCount := b
		for i := 0; i < a-2; i++ {
			if seat[i] == seat[i+2] && seat[i] != seat[i+1] {
				seat[i+1] = seat[i]
				changeCount--
			}
			if changeCount == 0 {
				break
			}
		}

		if changeCount > 0 {
			for i := 1; i < a-1; i++ {
				if seat[i] != seat[i+1] {
					seat[i+1] = seat[i]
				}
			}
		}

		s := seat[0]

		for i := 1; i < a; i++ {
			if s == seat[i] {
				ans++
			}
			s = seat[i]
		}

	}
	fmt.Println(ans)
}

func spritString(input string) (res []string) {
	for i := 0; i < utf8.RuneCountInString(input); i++ {
		res = append(res, input[i:i+1])
	}
	return
}