using System;

public class Program {
	public static void Main(string[] args) {
		int n = int.Parse(Console.ReadLine());
		TimeSpan timeSpan = new TimeSpan(0, 0, 0);
		for (int i = 0; i < n; i++) {
			string[] s = Console.ReadLine().Split(' ');
			DateTime a = DateTime.Parse(s[0]);
			DateTime b = DateTime.Parse(s[1]);
			if (a > b) {
				b = b.AddHours(24);
			}
			timeSpan += b - a;
		}
		Console.WriteLine(timeSpan.TotalMinutes);
	}
}