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 Haskell (GHC 7.10.3) (judge verdict: Wrong Answer)

import Data.List

main :: IO ()
main = do
  k <- last . map read . words <$> getLine
  s <- getLine
  print $ solve k s

solve :: Int -> String -> Int
solve k s = go 0 k (length $ group s) + count s
  where
    go acc 0 _ = acc
    go acc _ 1 = acc
    go acc _ 2 = 1 + acc
    go acc k n =  go (acc + 2) (k - 1) (n - 1)

count :: String -> Int
count s = go 0 'X' s
  where
    go acc _ [] = acc
    go acc 'R' ('R':s) = go (acc + 1) 'R' s
    go acc 'L' ('L':s) = go (acc + 1) 'L' s
    go acc _ (c:s) = go acc c s