import java.util.Scanner;

public class No70 {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();

        int result = 0;

        for (int i = 0; i < n; i++) {
            String sleep = sc.next();
            String[] sleeps = sleep.split(":");
            int sleepH = Integer.parseInt(sleeps[0]);
            int sleepM = Integer.parseInt(sleeps[1]);

            String wakeup = sc.next();
            String[] wakeups = wakeup.split(":");
            int wakeupH = Integer.parseInt(wakeups[0]);
            int wakeupM = Integer.parseInt(wakeups[1]);

            int time = ((wakeupH * 60) + wakeupM) - ((sleepH * 60) + sleepM);

            if (time < 0) {
                time += (60 * 24);
            }

            result += time;
        }

        System.out.println(result);

        sc.close();
    }

}