import java.util.Calendar;
import java.util.Scanner;

class Timer {
	int sleepH, sleepM, wakeUpH, wakeUpM;

	public Timer(String[] s) {
		int[] num = new int[4];

		for (int i = 0; i < s.length; i++) {
			num[i] = Integer.parseInt(s[i]);
		}

		this.sleepH = num[0];
		this.sleepM = num[1];
		this.wakeUpH = num[2];
		this.wakeUpM = num[3];

		if (this.sleepH > this.wakeUpH) {
			this.wakeUpH += 24;
		}
		else if(this.sleepH == this.wakeUpH){
			if(this.sleepM > this.wakeUpM){
				this.wakeUpH += 24;
			}
		}
	}
}

class Converter {
	public static int minute(Calendar calendar) {
		int day = calendar.get(Calendar.DATE);
		int hour = calendar.get(Calendar.HOUR_OF_DAY);
		int minute = calendar.get(Calendar.MINUTE);

		return (day - 1) * 1440 + hour * 60 + minute;
	}
}

public class No_70 {

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

		Calendar sleep = Calendar.getInstance();
		Calendar wakeUp = Calendar.getInstance();
		Timer timer;
		String[] s;
		int sleepMinute = 0, wakeUpMinute = 0, sleeping = 0;

		for (int i = 0; i < n; i++) {
			s = dismantle(sc.nextLine());
			
			timer = new Timer(s);
			sleep.set(2016, 0, 1, timer.sleepH, timer.sleepM, 0);
			wakeUp.set(2016, 0, 1, timer.wakeUpH, timer.wakeUpM, 0);

			sleepMinute = Converter.minute(sleep);
			wakeUpMinute = Converter.minute(wakeUp);

			sleeping += wakeUpMinute - sleepMinute;
		}

		System.out.println(sleeping);
		sc.close();

	}

	public static String[] dismantle(String s) {
		s = s.replaceAll(":", " ");
		String[] ns = s.split(" ");
		return ns;

	}

}