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)

n,k = map(int,input().split())
s = list(input())

l = 0
r = 0
count = 0
hcount = 0
score = 0
def sccount(s):
    l = 0
    r = 0
    count = 0
    score = 0
    for i in range(n):
        if s[i] == 'R':
            if r == 1:
                score += 1
            l = 0
            r = 1
        else:
            if l == 1:
                score += 1
            l = 1
            r = 0
    l = 0
    r = 0
    return score

if s[0] == 'L':
    for i in range(n):
        if s[i] == 'L':
            if r == 1 :
                count += 1
            l = 1
            r = 0
        else:
            l = 0
            r = 1
    if s[-1] == 'R':
        hcount = 1
else:
    for i in range(n):
        if s[i] == 'R':
            if l == 1 :
                count += 1
            l = 0
            r = 1
        else:
            l = 1
            r = 0
    if s[-1] == 'L':
        hcount = 1
score = sccount(s)
if count >= k:
    ans = score + k*2
elif count < k:
    ans = score + count*2 + hcount
print(ans)
# print(score,count,hcount)