package no070;

import java.util.Scanner;

public class Main {

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

}