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

class Program
{
    const int YEAR = 2019;
    const int MONTH = 1;
    const int DAY = 1;
    static void Main(string[] args)
    {
        var n = int.Parse(Console.ReadLine());
        var input = new List<string>();
        var t1 = new List<int>();
        var t2 = new List<int>();
        int h1 = 0, h2 = 0, m1 = 0, m2 = 0;

        int sleepTime = 0;
        for (int i = 0; i < n; i++)
        {
            input = Console.ReadLine().Split(' ').ToList();
            t1 = input[0].Split(':').Select(x => int.Parse(x)).ToList();
            t2 = input[1].Split(':').Select(x => int.Parse(x)).ToList();
            h1 = t1[0];
            m1 = t1[1];
            h2 = t2[0];
            m2 = t2[1];
            var dt1 = new DateTime(YEAR, MONTH, DAY, h1, m1, 0);
            var dt2 = new DateTime(YEAR, MONTH, DAY, h2, m2, 0);
            dt2 = dt2.AddHours(-h1);
            dt2 = dt2.AddMinutes(-m1);
            sleepTime += (dt2.Hour * 60) + dt2.Minute;
        }
        Console.WriteLine(sleepTime);
    }
}