using System;

public class Program

{

    public static void Main()

    {

        var passengers = int.Parse(Console.ReadLine());

        var stops = int.Parse(Console.ReadLine());

        int get = 0;

        int getout = 0;

        int all = 0;

        for (int i = 0;1< stops; i++)

        {

            if(1 % 2==0)

            {

                getout = int.Parse(Console.ReadLine());

                get = int.Parse(Console.ReadLine());

                all = (passengers - getout) + get +2;

            }

            else

            {

                getout = int.Parse(Console.ReadLine());

                all = all - (getout + 2);

            }

        }

        int getin = int.Parse(Console.ReadLine());

        int end = all + getin;

        Console.WriteLine($"The final number of passengers is : {end}");

    }

}