using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using BitArray = System.Collections.BitArray;
using BigInteger = System.Numerics.BigInteger;
using TextReader = System.IO.TextReader;

namespace AtCoderProject
{
    public class Program
    {
        public object Calc()
        {
            var N = consoleReader.Int;
            var K = consoleReader.Int;
            var wests = consoleReader.String.Select(c => c == 'L').ToArray();

            //var westEdge = wests[0];
            //var eastEdge = !wests[wests.Length - 1];
            var count = 1;
            var current = wests[0];
            var list = new List<int>();

            for (int i = 1; i < N; i++)
            {
                if (current == wests[i])
                    count++;
                else
                {
                    list.Add(count);
                    count = 1;
                    current = wests[i];
                }
            }
            list.Add(count);
            var grouped = list.ToArray();
            var sums = new int[grouped.Length + 1];
            sums[0] = 0;
            for (int i = 0; i < grouped.Length; i++)
                sums[i + 1] = sums[i] + grouped[i];

            var k2 = 2 * K + 1;
            if (sums.Length <= k2)
                return sums[sums.Length - 1] - 1;

            var l = -1;
            var r = -1;

            var max = 0;
            for (int i = k2; i < sums.Length; i++)
            {
                var tmp = sums[i] - sums[i - k2];
                if (tmp > max)
                {
                    l = i - k2;
                    r = i - 1;
                    max = tmp;
                }
            }

            var res = 0;
            for (int i = 0; i < grouped.Length; i++)
            {
                if (i == l)
                {
                    res += max -1;
                    i = r;
                }
                else
                {
                    res += grouped[i] -1;
                }
            }

            return res;
        }


        #region いつもの
        private readonly ConsoleReader consoleReader;
        public Program(ConsoleReader consoleReader) { this.consoleReader = consoleReader; }
        static void Main() => Console.WriteLine(new Program(new ConsoleReader(Console.In)).Calc()); static string AllLines<T>(IEnumerable<T> source) => string.Join("\n", source);
        #endregion
    }
#pragma warning disable
    public class ConsoleReader
    {
        private string[] ReadLineSplit() => textReader.ReadLine().Split(Array.Empty<char>(), StringSplitOptions.RemoveEmptyEntries);
        private string[] line = Array.Empty<string>();
        private int linePosition;
        private TextReader textReader;
        public ConsoleReader(TextReader tr) { textReader = tr; }
        public int Int => int.Parse(String);
        public long Long => long.Parse(String);
        public double Double => double.Parse(String);
        public string String
        {
            get
            {
                if (linePosition >= line.Length)
                {
                    linePosition = 0;
                    line = ReadLineSplit();
                }
                return line[linePosition++];
            }
        }
        public class SplitLine
        {
            private string[] splited;
            public SplitLine(ConsoleReader cr) { splited = cr.ReadLineSplit(); cr.line = Array.Empty<string>(); }
            public int[] Int => String.Select(x => int.Parse(x)).ToArray();
            public int[] Int0 => String.Select(x => int.Parse(x) - 1).ToArray();
            public long[] Long => String.Select(x => long.Parse(x)).ToArray();
            public double[] Double => String.Select(x => double.Parse(x)).ToArray();
            public string[] String => splited;
        }
        public SplitLine Split => new SplitLine(this);
        public class RepeatReader : IEnumerable<ConsoleReader>
        {
            ConsoleReader cr; int count;
            public RepeatReader(ConsoleReader cr, int count) { this.cr = cr; this.count = count; }
            public IEnumerator<ConsoleReader> GetEnumerator() => Enumerable.Repeat(cr, count).GetEnumerator();
            System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() => GetEnumerator();

            public IEnumerable<string> String => this.Select(cr => cr.String);
            public IEnumerable<int> Int => this.Select(cr => cr.Int);
            public IEnumerable<int> Int0 => this.Select(cr => cr.Int - 1);
            public IEnumerable<long> Long => this.Select(cr => cr.Long);
            public IEnumerable<double> Double => this.Select(cr => cr.Double);
        }
        public RepeatReader Repeat(int count) => new RepeatReader(this, count);
    }
}

Measured memory_bytes: 14048