/* ID: thanhvq1
LANG: C++14
PROB: namenum
*/

//#pragma GCC optimize ("O2")
#include<bits/stdc++.h>
#include<unistd.h>
using namespace std;

// defines
#define int long long
typedef long long ll;
//#define double long double
#define vec vector
#define vi vector<int>
#define vvi vector<vector<int>>
#define ii pair<int, int>
#define vii vector<ii>
#define F first
#define S second
#define MP make_pair
#define PB push_back
#define ALL(x) begin(x),end(x)
#define SZ(x) ((int)(x).size())
#define FOR(i, a, b) for(int i = (a); i < (b); i++)
#define FORE(i, a, b) for(int i = (a); i <= (b); i++)
#define FORD(i, a, b) for(int i = (a); i >= (b); i--)
//#define UNI(x) (x).resize(unique((x).begin(), (x).end()) - (x).end());
#define SORT_UNIQUE(c) (sort(c.begin(),c.end()), c.resize(distance(c.begin(),unique(c.begin(),c.end()))))
#define GET_POS(c,x) (lower_bound(c.begin(),c.end(),(x))-c.begin())
#define MS0(X) memset((X), 0, sizeof((X)))
#define MS1(X) memset((X), -1, sizeof((X)))
#define RESET(X, y) memset(X, y, sizeof(X))
#define chkmin(a, b) a = min(a, b)
#define chkmax(a, b) a = max(a, b)
#define max3(a, b, c) max({a, b, c})
#define min3(a, b, c) min({a, b, c})
#define debug(x) cout << #x << " = " << (x) << endl
#define debug2(x, y) cout<<#x<<" = "<<(x)<<", "<<#y<<" = "<<(y)<< endl
#define debug3(x, y, z) cout<<#x<<" = "<<(x)<<", "<<#y<<" = "<<(y)<<", "<<#z<<" = "<<(z)<<endl
void debug_out() { cerr << endl; }
template <typename H, typename... T> void debug_out(H h, T... t) {  cerr << " " << (h);  debug_out(t...); }
#define DEBUG(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
//#define CASET int ___T; scanf("%d", &___T); for(int cs=1;cs<=___T;cs++)

//permanent constants
const long long INF64 = 1e18; const int INF32 = 1e9; const int BIG = (int)(1e9 + 239);
const int MOD = 998244353; //1e9 + 7;  const ll MOD2 = (ll)MOD * (ll)MOD;
const double PI = 2.0*acos(0.0); //acos(-1.0L);
const double EPS = static_cast<double>(1e-10);
const int day[12] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
const int dx[4] = {0, 1, 0, -1}; const int dy[4] = {1, 0, -1, 0};

//random
mt19937 rnd(239); //(chrono::high_resolution_clock::now().time_since_epoch().count());

typedef vector<vector<int>> matrix;   //matrix Z(n, vector<LL>(n));

/*GRAPH:
	vector<vector<int>> dist; // ma tran dist giua cac dinh
    dist.assign(N, vector<int>(N, INF)); // Khoi tao ma tran dist bang INF
*/
// Sort w Lambda Function: sort(begin(v), end(v), [] (int a, int b) { return a > b; });

void FILEIO() {  freopen("in.txt", "r", stdin);  freopen("out.txt", "w", stdout); }
//void FILEIO()   {freopen("in.txt", "w", stdout);}
//void FILEIO() {  freopen("namenum.in", "r", stdin);  freopen("namenum.out", "w", stdout); }

//Tricks:
#define odd(x) ((x) & 1)
#define even(x) !((x) & 1)

int mostSignDigit(int n) { double k = log10(n); return pow(10, k-floor(k));}
int numOfDigits(int n) {return floor(log10(n)) + 1;}
bool isPowerOfTwo(int x) {return x && (!(x&(x-1)));} // first x is for the case x=0

bool allPositive(vector<int> &a) {return all_of(begin(a), end(a), [](int x){return x > 0;});} // are all of the elements positive?
bool anyPositive(vector<int> &a) {return any_of(begin(a), end(a), [](int x){return x > 0;});} // is there at least one positive element?
bool nonePositive(vector<int> &a) {return none_of(begin(a), end(a), [](int x){return x > 0;});} // are none of the elements positive?

// Init variables here

void solve() {
	int n, k; string s; cin >> n >> k >> s;
	int lr=0, rl=0, happy = 0;
	FOR(i, 0, n-1) {
		if(s[i]=='L' and s[i+1]=='R') lr++;
		if(s[i]=='R' and s[i+1]=='L') rl++;
		if(s[i]==s[i+1]) happy++;


//		debug3(i, s[i], s[i+1]); debug2(lr, rl);
//		debug3(s[i], s[i+1], happy);

	}
	int m = min(rl, lr);

//	debug3(rl, lr, m);

	if(k<=m) happy += 2*min(k, m);
	if(k>m) {
		happy += 2*m;
		if(rl!=lr) happy++;
	}

//	debug3(k, m, happy);

	cout << happy << endl;
}

signed main() {
  ios_base::sync_with_stdio(false); cin.tie();
//  FILEIO();
//  auto beginProgram = chrono::steady_clock::now();

//  cin >> n;
//  int test=0;
//  while(n)
  {
//	  input();
//	  cout << "Case " << ++test << ":" << endl;
	  solve();
  }

//  auto endProgram = chrono::steady_clock::now();
//  cout << chrono::duration_cast<chrono::milliseconds>(endProgram - beginProgram).count() << " ms" << endl;

  return 0;
}


Measured memory_bytes: 512