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

namespace AtCoder
{
    class Program
    {
        static void Main(string[] args)
        {
            var sw = new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
            Console.SetOut(sw);
            new Program().Solve(new ConsoleInput(Console.In, ' '));
            Console.Out.Flush();
#if DEBUG
            ReadLine();
#endif
        }


        void Solve(ConsoleInput cin)
        {
            int n = cin.ReadInt;
            int q = cin.ReadInt;

            string s = cin.Read;
            List<Tuple<char, bool>> query = new List<Tuple<char, bool>>();
            for (int i = 0; i < q; i++)
            {
                char c = cin.Read[0];
                bool b = cin.Read == "R"; //true R, false L
                query.Add(new Tuple<char, bool>(c, b));
            }
            query.Reverse();

            char lastRight = (char)0;
            char right = s[n - 1];
            char lastLeft = (char)0;
            char left = s[0];
            int rightCnt = 0;
            int leftCnt = 0;
            int maxRightCnt = 0;
            int maxLeftCnt = 0;
            for (int j = 0; j < q; j++)
            {
                //右から落ちる
                if (query[j].Item1 == right)
                {
                    if (query[j].Item2)
                    {
                        rightCnt++;
                        if (n - rightCnt - 1 >= 0)
                        {
                            lastRight = right;
                            right = s[n - rightCnt - 1];
                        }
                    }
                }
                else if (query[j].Item1 == lastRight)
                {
                    if (!query[j].Item2)
                    {
                        rightCnt = 0;
                        lastRight = (char)0;
                        right = s[n - 1];
                    }
                }

                //左から落ちる
                if (query[j].Item1 == left)
                {
                    if (!query[j].Item2)
                    {
                        leftCnt++;
                        if (leftCnt < n)
                        {
                            lastLeft = left;
                            left = s[leftCnt];
                        }
                    }
                }
                else if (query[j].Item1 == lastLeft)
                {
                    if (query[j].Item2)
                    {
                        leftCnt = 0;
                        lastLeft = (char)0;
                        left = s[0];
                    }
                }
                if (maxRightCnt < rightCnt)
                    maxRightCnt = rightCnt;
                if (maxLeftCnt < leftCnt)
                    maxLeftCnt = leftCnt;
            }

            if (maxLeftCnt + maxRightCnt < n)
            {
                Console.WriteLine(n - (maxLeftCnt + maxRightCnt));
            }
            else
            {
                Console.WriteLine(0);
            }
        }

        class ConsoleInput
        {
            private readonly System.IO.TextReader _stream;
            private char _separator = ' ';
            private Queue<string> inputStream;

            public ConsoleInput(System.IO.TextReader stream, char separator = ' ')
            {
                this._separator = separator;
                this._stream = stream;
                inputStream = new Queue<string>();
            }

            public string Read
            {
                get
                {
                    if (inputStream.Count != 0) return inputStream.Dequeue();
                    string[] tmp = _stream.ReadLine().Split(_separator);
                    for (int i = 0; i < tmp.Length; ++i)
                        inputStream.Enqueue(tmp[i]);
                    return inputStream.Dequeue();
                }
            }

            public string ReadLine { get { return _stream.ReadLine(); } }
            public int ReadInt { get { return int.Parse(Read); } }
            public long ReadLong { get { return long.Parse(Read); } }
            public double ReadDouble { get { return double.Parse(Read); } }
            public string[] ReadStrArray(long N) { var ret = new string[N]; for (long i = 0; i < N; ++i) ret[i] = Read; return ret; }
            public int[] ReadIntArray(long N) { var ret = new int[N]; for (long i = 0; i < N; ++i) ret[i] = ReadInt; return ret; }
            public long[] ReadLongArray(long N) { var ret = new long[N]; for (long i = 0; i < N; ++i) ret[i] = ReadLong; return ret; }
        }
    }
}