04. Bus

import java.util.Scanner;

public class Bus_04 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

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

        for (int stop = 1; stop <= stops ; stop++) {
            int outCount = Integer.parseInt(scanner.nextLine());
            int inCount = Integer.parseInt(scanner.nextLine());

            startCount -= outCount;
            startCount += inCount;

            if(stop % 2 == 1){
                startCount += 2;
            } else {
                startCount -= 2;
            }
        }

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