import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int ans = 0;
		for(int i = 0 ; i < n ; i++) {
			String[] temp = (sc.next() + ":" + sc.next()).split("[\\:]");
			int[] time = {Integer.valueOf(temp[0]), Integer.valueOf(temp[1])
					    , Integer.valueOf(temp[2]), Integer.valueOf(temp[3])};
			int st = time[0] * 60 + time[1];
			int en = (time[2] * 60 + time[3]) + 24 * 60;
			ans += (en - st) % (24 * 60);
		}
		System.out.println(ans);
 	}
}