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: Accepted)

package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

func solve() {
	n, k := getInt(), getInt()
	s := []rune(getString())

	cnt := 0
	sum := 0
	now := ' '
	for i, r := range s {
		if r != now {
			now = r
			sum += cnt
			cnt = 0
		} else {
			cnt++
			if i == n-1 {
				sum += cnt
			}
		}
	}

	ans := min(n-1, sum+(2*k))
	fmt.Fprintln(wr, ans)
}

func min(a, b int) int {
	if a < b {
		return a
	}
	return b
}

// -----------------------------------------

var (
	sc = bufio.NewScanner(os.Stdin)
	wr = bufio.NewWriter(os.Stdout)
)

func main() {
	buf := 200001
	sc.Buffer(make([]byte, buf), buf)
	sc.Split(bufio.ScanWords)
	solve()
	wr.Flush()
}

func getInt() int {
	sc.Scan()
	i, err := strconv.Atoi(sc.Text())
	if err != nil {
		panic(err)
	}
	return i
}

func getIntSlice(n int) []int {
	is := make([]int, n)
	for i := range is {
		is[i] = getInt()
	}
	return is
}

func getString() string {
	sc.Scan()
	s := sc.Text()
	return s
}