package TestApril14_15;

import java.util.Scanner;

public class Bus {
    public static void main(String[] agrs) {
        Scanner scanner = new Scanner(System.in);

        int passengersInStart = Integer.parseInt(scanner.nextLine());
        int stops = Integer.parseInt(scanner.nextLine());

        int leftPassengers = passengersInStart;

        for (int i = 1; i <= stops; i++) {
            int s = Integer.parseInt(scanner.nextLine());
            int k = Integer.parseInt(scanner.nextLine());

            if (i % 2 == 1) {
                leftPassengers = leftPassengers - s;
                leftPassengers = leftPassengers + k  + 2;
            } else {
                leftPassengers = leftPassengers - s - 2;
                leftPassengers = leftPassengers + k ;
            }

        }
        System.out.printf("The final number of passengers is : %d", leftPassengers);
    }
}