Bus

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int passengers = Integer.parseInt(scanner.nextLine()),
                stations = Integer.parseInt(scanner.nextLine()),
                outputPassengers, inputPassengers;

        for (int i = 1; i <= stations; i++) {
            outputPassengers = Integer.parseInt(scanner.nextLine());
            inputPassengers = Integer.parseInt(scanner.nextLine());
            passengers += inputPassengers - outputPassengers;

            if (i % 2 == 1) {
                passengers += 2;
            } else {
                passengers -= 2;
            }
        }

        System.out.println("The final number of passengers is : " + passengers);
    }
}