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"
	"io"
	"os"
	"strconv"
)

type MyScanner struct {
	sc *bufio.Scanner
}

type MyWriter struct {
	stdout io.Writer
}

type MyPut interface{}

func getScanner(fp io.Reader) *bufio.Scanner {
	sc := bufio.NewScanner(fp)
	sc.Split(bufio.ScanWords)
	sc.Buffer(make([]byte, 500001), 500000)
	return sc
}

func getHugeScanner(fp io.Reader, size int) *bufio.Scanner {
	sc := bufio.NewScanner(fp)
	sc.Split(bufio.ScanWords)
	sc.Buffer(make([]byte, size), size)
	return sc
}

func (mysc *MyScanner)String() string {
	mysc.sc.Scan()
	return mysc.sc.Text()
}

func (mysc *MyScanner)Int() int {
	i, _ := strconv.Atoi(mysc.String())
	return i
}

func (mysc *MyScanner)Int64() int64 {
	i, _ := strconv.ParseInt(mysc.String(), 10, 64)
	return i
}

func (mysc *MyScanner)Float64() float64 {
	i, _ := strconv.ParseFloat(mysc.String(), 64)
	return i
}

func (mw MyWriter)Puts(v MyPut) {
	_, _ = fmt.Fprintf(mw.stdout, "%v\n", v)
}

func Solve(stdin io.Reader, stdout io.Writer) {
	sc := MyScanner{getHugeScanner(stdin, 100008)}
	mw := MyWriter{stdout}

	n := sc.Int()
	k := sc.Int()
	s := sc.String()

	var l []int

	var b uint8 =  'X'

	for i := 0; i < n; i++ {
		if s[i] == b {
			l[len(l) - 1]++
		} else {
			l = append(l, 1)
		}
		b = s[i]
	}

	if k < len(l) / 2 {
		ans := 0
		for i := 0; i < len(l); i++ {
			ans += l[i] - 1
		}
		ans += k * 2
		mw.Puts(ans)
	} else {
		mw.Puts(n - 1)
	}

}

func main() {
	Solve(os.Stdin, os.Stdout)
	return
}