using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace Competitive
{
    internal class Solution
    {
        public int N, M;
        public Data[] D;
        public int[] R;

        public void Run()
        {
            // Input
            {
                var line = Input.ReadIntArray();
                N = line[0];
                M = line[1];
            }

            D = new Data[M];
            for (int i = 0; i < M; i++)
            {
                var line = Console.ReadLine();
                D[i] = new Data(line);
            }

            // Sort
            Array.Sort(D, (d1, d2) => (d1.O.CompareTo(d2.O)));

            // Set Rooms
            R = new int[N];
            for (int i = 0; i < N; i++) R[i] = -1;

            // Solve
            int ret = 0;

            for (int i = 0; i < M; i++)
            {
                int last_room = -1;
                int last_t = -2;

                for (int j = 0; j < N; j++)
                {
                    // チェックイン時刻には空いており、かつ条件を満たす者の中で最も遅い
                    if (R[j] < D[i].I && R[j] > last_t)
                    {
                        last_room = j;
                        last_t = R[j];
                    }
                }

                if (last_room != -1)
                {
                    R[last_room] = D[i].O;
                    ret++;
                }
            }

            Console.WriteLine(ret);
        }
    }

    // libs ----------
    class Data
    {
        public int I, O;

        public Data(string line)
        {
            int ID = int.Parse(line.Substring(0, 1));
            int IH = int.Parse(line.Substring(2, 2));
            int IM = int.Parse(line.Substring(5, 2));
            int OD = int.Parse(line.Substring(8, 2));
            int OH = int.Parse(line.Substring(10, 2));
            int OM = int.Parse(line.Substring(13, 2));
            I = ID * 24 * 60 + IH * 60 + IM;
            O = OD * 24 * 60 + OH * 60 + OM;
        }
    }

    // common ----------

    internal static class Input
    {
        public static int ReadInt()
        {
            string line = Console.ReadLine();
            return int.Parse(line);
        }

        public static int[] ReadIntArray()
        {
            string line = Console.ReadLine();
            return line.Split(' ').Select(int.Parse).ToArray();            
        }

        public static double[] ReadDoubleArray()
        {
            string line = Console.ReadLine();
            return line.Split(' ').Select(double.Parse).ToArray();
        }

        public static long[] ReadLongArray()
        {
            string line = Console.ReadLine();
            return line.Split(' ').Select(long.Parse).ToArray();
        }
    }
    
    internal class Program
    {
        public static void Main(string[] args)
        {
            var s = new Solution();
            s.Run();
        }
    }
}