using System;
using System.Linq;

public class Program
{
	public static void Main()
	{
		int N = int.Parse(Console.ReadLine());
		int ans = 0;
		for (int i = 0; i < N; i++)
		{
			string[] time = Console.ReadLine().Split();
			int[] sleep = time[0].Split(':').Select(j => int.Parse(j))
				.ToArray();
			int sleep_minute = sleep[0] * 60 + sleep[1];
			int[] wakeUp = time[1].Split(':').Select(j => int.Parse(j))
				.ToArray();
			int wakeUp_minute = wakeUp[0] * 60 + wakeUp[1];
			if (sleep_minute > wakeUp_minute)
			{
				wakeUp_minute += 24 * 60;
			}
			ans += wakeUp_minute - sleep_minute;
		}
		Console.WriteLine(ans);
	}
}