using System;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static void Main(string[] args)
    {
        int n = int.Parse(Console.ReadLine());

        int hour = 0;
        int minute = 0;

        string[] time;
        int[] before;
        int[] after;

        for (int i = 0; i < n; i++)
        {
            time = Console.ReadLine().Split();
            before = time[0].Split(':').Select(v => int.Parse(v)).ToArray();
            after = time[1].Split(':').Select(v => int.Parse(v)).ToArray();

            if (after[0] < before[0])
            {
                hour += 24 - before[0];
                hour += after[0];
            }
            else
            {
                hour += after[0] - before[0];
            }

            if (after[1] != before[1])
            {
                hour--;
                minute += 60 - before[1];
                minute += after[1];
            }
        }

        Console.WriteLine(hour * 60 + minute);
        Console.ReadLine();

    }
}