class Program
{
    static void Main(string[] args)
    {
        int count = int.Parse(Console.ReadLine()!);
        int sleepMinute = 0;
        int sleepHour = 0;

        for (int i = 0; i < count; i++)
        {
            string[] input = Console.ReadLine()!.Split(' ');
            TimeSpan start = TimeSpan.Parse(input[0]);
            TimeSpan wakeup = TimeSpan.Parse(input[1]);

            int startHour = start.Hours;
            int wakeupHour = wakeup.Hours;
            int startMinute = start.Minutes;
            int wakeupMinute = wakeup.Minutes;

            if (startHour == wakeupHour && startMinute < wakeupMinute)
            {
                sleepMinute = wakeupMinute - startMinute;
            }
            else if(startHour == wakeupHour && startMinute > wakeupMinute)
            {
                sleepHour += 23;
                sleepMinute = 60 - wakeupMinute;
            }
            else if(startMinute != wakeupMinute)
            {
                sleepMinute += 60 - startMinute + wakeupMinute;
            }

            if (wakeupHour < startHour)
            {
                sleepHour += 23 - startHour + wakeupHour;
            }
            else
            {
                sleepHour += wakeupHour - startHour;
            }
            
            if (sleepMinute >= 60)
            {
                sleepHour += 1;
                sleepMinute -= 60;
            }

        }

        Console.WriteLine(sleepHour * 60 + sleepMinute);
    }
}