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

class Magatro
{
    static void Main()
    {
        int N = int.Parse(Console.ReadLine());
        int cnt = 0;
        for(int i = 0; i < N; i++)
        {
            int[] a = Console.ReadLine().Split(' ', ':').Select(s => int.Parse(s)).ToArray();
            int time = 0;
            if (a[0] > a[2])
            {
                time = 60 * (a[2] + 24 - a[0]) + a[3] - a[1];
            }
            else if(a[0]<a[2])
            {
                time = 60 * (a[2] - a[0]) + a[3] - a[1];
            }
            else
            {
                if (a[3] >= a[1])
                {
                    time = a[3] - a[1];
                }
                else
                {
                    time = 60 * 24 + a[3] - a[1];
                }
            }
            cnt += time;
        }
        Console.WriteLine(cnt);
    }
}