import java.util.Scanner;

public class Yukicoder70 {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		String s;
		String[] buf, buf2;
		int h1, m1, h2, m2;
		int sum = 0;
		for (int i = 0; i < n; i++) {
			buf = sc.next().split(":");
			h1 = Integer.parseInt(buf[0]);
			m1 = Integer.parseInt(buf[1]);
			buf = sc.next().split(":");
			h2 = Integer.parseInt(buf[0]);
			m2 = Integer.parseInt(buf[1]);

			sum += h1 > h2 ? (h2 - h1 + 24) * 60 : (h2 - h1) * 60;
			sum += m2 - m1;
		}
		System.out.println(sum);
	}
}