using System;
using System.Collections.Generic;
using System.Linq;
using static System.Console;
using static System.Math;
using static System.Array;

class MainClass : Scanner
{
    static void Main()
    {
        var (N, K) = ReadStream<int,int>();
        string S = RString();
        var LRCount = new List<int>();
        int now = 0;
        bool dir = false;
        while (now < N)
        {
            int cnt = 0;
            while (now < N && S[now] == 'L') { cnt++; now++; }
            if (cnt > 0) LRCount.Add(cnt);

            cnt = 0;
            while (now < N && S[now] == 'R') { cnt++; now++; }
            if (cnt > 0) LRCount.Add(cnt);
        }
        LRCount.Add(0);

        int sum = LRCount[0];
        LRCount[0] = 0;
        for (int i = 0; i < K&&i*2+2<LRCount.Count; i++)
        {
            int nw = i * 2 + 1;
            sum += LRCount[nw] + LRCount[nw + 1];
            LRCount[nw] = LRCount[nw + 1] = 0;
        }
        int ans = 0;
        ans += sum - 1;
        for (int i = 0; i < LRCount.Count; i++)
        {
            ans += Max(0, LRCount[i] - 1);
        }
        WriteLine(ans);
    }
}

class Scanner
{
    public static int RInt() => int.Parse(Console.ReadLine());
    public static long RLong() => long.Parse(Console.ReadLine());
    public static string RString() => Console.ReadLine();
    public static double RDouble() => double.Parse(Console.ReadLine());

    public static int[] RInts() => Array.ConvertAll(Console.ReadLine().Split(), int.Parse);
    public static int[] RInts(Func<string, int> func) => Console.ReadLine().Split().Select(func).ToArray();
    public static long[] RLongs() => Array.ConvertAll(Console.ReadLine().Split(), long.Parse);
    public static long[] RLongs(Func<string, long> func) => Console.ReadLine().Split().Select(func).ToArray();
    public static double[] RDoubles() => Array.ConvertAll(Console.ReadLine().Split(), double.Parse);
    public static double[] RDoubles(Func<string, double> func) => Console.ReadLine().Split().Select(func).ToArray();
    public static string[] RStrings() => Console.ReadLine().Split();
    //public static string[] RStrings(Func<string, string> func) => Console.ReadLine().Split().Select(func).ToArray();
    public static T1 ReadStream<T1>()
    {
        var r = RStrings();
        var r1 = (T1)Convert.ChangeType(r[0], typeof(T1));
        return r1;
    }
    public static (T1, T2) ReadStream<T1, T2>()
    {
        var r = RStrings();
        var r1 = (T1)Convert.ChangeType(r[0], typeof(T1));
        var r2 = (T2)Convert.ChangeType(r[1], typeof(T2));
        return (r1, r2);
    }
    public static (T1, T2, T3) ReadStream<T1, T2, T3>()
    {
        var r = RStrings();
        var r1 = (T1)Convert.ChangeType(r[0], typeof(T1));
        var r2 = (T2)Convert.ChangeType(r[1], typeof(T2));
        var r3 = (T3)Convert.ChangeType(r[2], typeof(T3));
        return (r1, r2, r3);
    }
    public static (T1, T2, T3, T4) ReadStream<T1, T2, T3, T4>()
    {
        var r = RStrings();
        var r1 = (T1)Convert.ChangeType(r[0], typeof(T1));
        var r2 = (T2)Convert.ChangeType(r[1], typeof(T2));
        var r3 = (T3)Convert.ChangeType(r[2], typeof(T3));
        var r4 = (T4)Convert.ChangeType(r[3], typeof(T4));
        return (r1, r2, r3, r4);
    }
}

Measured memory_bytes: 29108