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 Java8 (OpenJDK 1.8.0) (judge verdict: Wrong Answer)

import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        // Your code here!
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int k = sc.nextInt();
        String str = sc.next();
        char c[] = str.toCharArray();
        char dir = c[0];
        
        int begin = 0;
        int end = n - 1;
        int flag = 0;
        for (int i = 0; i < n; i++) {
            if (dir != c[i]) {
                if (flag == 0) {
                    begin = i;
                    if (dir == 'L') {
                        dir = 'R';
                    } else {
                        dir = 'L';
                    }
                    flag = 1;
                } else {
                    end = i;
                    dir = c[i];
                    for (int j = begin; j < end; j++) {
                        c[j] = dir;
                    }
                    begin = i;
                    end = n - 1;
                    k--;
                    flag = 0;
                }
            }
            
            if (k == 0) {
                break;
            }
        }
        
        if (k > 0) {
            if (dir == 'L') {
                dir = 'R';
            } else {
                dir = 'L';
            }
            
            for (int i = begin; i < n; i++) {
                c[i] = dir;
            }            
        }
        
        int count = 0;
        for (int i = 0; i < n; i++) {
            if (c[i] == 'L') {
                if (i == 0) continue;
                if (c[i - 1] == c[i]) {
                    count++;
                }
            } else {
                if (i == n - 1) continue;
                if (c[i + 1] == c[i]) {
                    count++;
                }
            }
        }
        
        System.out.println(count);
    }
}