using System;
using System.IO;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
using System.Numerics;
using System.Diagnostics;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading.Tasks;
using static System.Math;
using static System.Console;


namespace yukicoder
{
    class Program
    {
        static void Main()
        {
            var n = int.Parse(Console.ReadLine());
            var day = 1440;
            var sleep = 0;

            for (int i = 0; i < n; i++)
            {
                var t = Console.ReadLine().Split(' ');
                var t1 = t[0].Split(":");
                var t2 = t[1].Split(":");

                var startHour = int.Parse(t1[0]) * 60;
                var startMinute = int.Parse(t1[1]);
                var endHour = int.Parse(t2[0]) * 60;
                var endMinute = int.Parse(t2[1]);

                if (startHour > endHour)
                {
                    sleep += day - ((startHour + startMinute) - (endHour + endMinute));
                }
                else
                {
                    sleep += (endHour + endMinute) - (startHour + startMinute);
                }
            }

            Console.WriteLine(sleep);

        }
        
    }
}