using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Szinezes
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] inp = Console.ReadLine().Split().Select(int.Parse).ToArray();
            int all = inp[0];
            int arusz = inp[1];
            int[] ball = new int[all + 1];
            for (int i = 0; i < arusz; i++)
            {
                inp = Console.ReadLine().Split().Select(int.Parse).ToArray();
                ball[inp[0]]++;
                ball[inp[1]]--;
            }
            int sol = 0;
            int bal = 0;
            int el = 0;
            for (int i = 0; i < all; i++)
            {
                el = bal;
                bal += ball[i];
                if (bal == 0 && el != 0)
                {
                    sol++;
                }
            }
            Console.WriteLine(sol);
            Console.ReadLine();
        }
    }
}