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 h = (Integer.valueOf(time[2]) + 24 - Integer.valueOf(time[0])) % 24;
			int m = Integer.valueOf(time[3]) - Integer.valueOf(time[1]);
			ans += h * 60 + m;
		}
		System.out.println(ans);
 	}
}