using System;
using static System.Console;
using System.Linq;
using System.Collections.Generic;
class Program
{
    static int NN => int.Parse(ReadLine());
    static int[] NList => ReadLine().Split().Select(int.Parse).ToArray();
    static int[][] NArr(long n) => Enumerable.Repeat(0, (int)n).Select(_ => NList).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var c = NList;;
        var (n, m) = (c[0], c[1]);
        var map = NArr(m);
        Array.Sort(map, (l, r) => l[1].CompareTo(r[1]));
        var pos = 1;
        var ans = 2 * n - 2;
        for (var i = 0; i < m; ++i)
        {
            if (pos <= map[i][0])
            {
                pos = map[i][1];
                --ans;
            }
        }
        WriteLine(ans);
    }
}