using System;
using System.Linq;

class Program
{
    static void Main(string[] args)
    {
        // No.70 睡眠の重要性！

        int N = int.Parse(Console.ReadLine());
        string sleep = "";
        DateTime timeFrom, timeTo;
        TimeSpan sleepSum = new TimeSpan();

        for (int i = 1; i <= N; i++)
        {
            sleep = Console.ReadLine();

            timeFrom = new DateTime(1, 1, 1,
                int.Parse(sleep.Split(' ')[0].Split(':')[0]),
                int.Parse(sleep.Split(' ')[0].Split(':')[1]),
                0);
            timeTo = new DateTime(1, 1, 1,
                int.Parse(sleep.Split(' ')[1].Split(':')[0]),
                int.Parse(sleep.Split(' ')[1].Split(':')[1]),
                0);
            if (timeFrom > timeTo) timeTo = timeTo.AddDays(1);

            sleepSum += timeTo - timeFrom;
        }

        Console.WriteLine((sleepSum.Days * 24 + sleepSum.Hours) * 60 + sleepSum.Minutes);
    }
}