using System;
using System.Linq;

class Program
{
    public void Solve()
    {
        int N = int.Parse(Console.ReadLine());
        string[] HMhm;
        int[] hm;

        TimeSpan time, sTime, eTime;
        int sleepTime = 0;

        for (int i = 0; i < N; i++)
        {
            HMhm = Console.ReadLine().Split(' ');

            hm = HMhm[0].Split(':').Select(s => int.Parse(s)).ToArray();
            sTime = new TimeSpan(hm[0], hm[1], 0);

            hm = HMhm[1].Split(':').Select(s => int.Parse(s)).ToArray();
            eTime = new TimeSpan(hm[0], hm[1], 0);

            time = (eTime - sTime < new TimeSpan(0, 0, 0) ? eTime - sTime + new TimeSpan(24, 0, 0) : eTime - sTime);

            sleepTime += time.Hours * 60 + time.Minutes;
        }

        Console.WriteLine(sleepTime);
    }

    static void Main()
    {
        var solver = new Program();
        solver.Solve();
    }
}