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 Python (3.4.3) (judge verdict: Accepted)

# https://atcoder.jp/contests/abc140/tasks/abc140_d

n, k = map(int, input().split())
str_n = input()
first = str_n[0]
last = ""
if first == "R":
    last = "L"
else:
    last = "R"

for count in range(k): 
    new_line = str_n
    next_last = new_line.find(last)
    next_first = new_line.find(first, next_last)
    next_line = new_line[0:next_last]
    if next_first != -1:
        next_line += new_line[next_last:next_first].replace(last, first) + new_line[next_first:]
    else:
        next_line += new_line[next_last:].replace(last, first)
    str_n = next_line

count = 0
result_line = str_n
for i in range(len(str_n) - 1):
    if result_line[i] == result_line[i + 1]:
        count += 1

print(count)