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 C++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include "bits/stdc++.h"

#define REP(i, a, b) for (ll i = (a); i <= (b); ++i)
#define REV(i, a, b) for (ll i = (a); i >= (b); --i)
#define FORV(a, A) for (auto &a : A)

using namespace std;

using ll = long long;

void Main()
{
   int N, K;
   cin >> N >> K;
   int k = 1;
   char S, prevS;
   cin >> prevS;
   if (prevS=='R') K--;
   REP(i, 1, N-1) {
      cin >> S;
      if (S!=prevS) {
         k++;
         swap(S, prevS);
      }
   }

   cout << min(N-k+2*K, N-2) << endl;
}

int main()
{
   std::cin.tie(nullptr);
   std::ios_base::sync_with_stdio(false);
   std::cout << std::fixed << std::setprecision(15);
   Main();
   return 0;
}