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[] time = (sc.next() + ":" + sc.next()).split(":");
			int st = Integer.valueOf(time[2]) * 60 + Integer.valueOf(time[3]);
			int en = Integer.valueOf(time[0]) * 60 + Integer.valueOf(time[1]);
			if(en < st) {
				en += 24 * 60;
			}
			ans += en - st;
		}
		System.out.println(ans);
 	}
}