neshto si

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

namespace Bus
{
    class Program
    {
        static void Main(string[] args)
        {
            int broiPassager = int.Parse(Console.ReadLine());
            int broiStops = int.Parse(Console.ReadLine());



            double smetka = 0;
            double counterPutnici = 0;
            double leftPasenger = 0;


            for (int currentStops = 1; currentStops <=broiStops; currentStops++)
            {
                double broiSlizashti = double.Parse(Console.ReadLine());
                double broiKachvat = double.Parse(Console.ReadLine());

                if (currentStops % 2 ==1)
                {
                     smetka = broiPassager - broiSlizashti + broiKachvat + 2;


                }
                else if (currentStops % 2 ==0)
                {
                     smetka = broiPassager - broiSlizashti - 2 + broiKachvat;

                }
                counterPutnici += smetka;

            }
            // counterPutnici += smetka;


        }
    }
}