import java.util.Scanner;

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

        int numOfPOnTheBusWhenItIsTakenOff = Integer.parseInt(scanner.nextLine());
        int numberOfStops = Integer.parseInt(scanner.nextLine());


        int totalPassengers = 0;

        for (int i = 1; i <= numberOfStops; i ++) {

            if(numberOfStops%2 != 0){
                int numOfPassengersGoingDown = Integer.parseInt(scanner.nextLine());
                int numOfPassengersPickedUp = Integer.parseInt(scanner.nextLine());
                totalPassengers = numOfPOnTheBusWhenItIsTakenOff - numOfPassengersGoingDown + numOfPassengersPickedUp + 2;

                }else if(numberOfStops%2 == 0){
                int numOfPassengersGoingDown = Integer.parseInt(scanner.nextLine());
                int numOfPassengersPickedUp = Integer.parseInt(scanner.nextLine());
                totalPassengers = totalPassengers - numOfPassengersGoingDown + numOfPassengersPickedUp - 2;
                numOfPOnTheBusWhenItIsTakenOff = totalPassengers;
            }
        }
        System.out.printf("The final number of passengers is: %d", totalPassengers);
    }
}