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

public class Program {
    public static int Solver(System.IO.TextReader reader) {
        var n = int.Parse( reader.ReadLine() );
        var totalAmount = 0;
        for (var i = 0; i != n; ++i) {
        var timespan = reader.ReadLine().Split( new[]{ ' ',':'} ).ToList().ConvertAll(int.Parse);
            var timeFrom = timespan[ 0 ] * 60 + timespan[ 1 ];
            var timeTill = timespan[ 2 ] * 60 + timespan[ 3 ];
            totalAmount += (timeTill>=timeFrom?timeTill:timeTill+24*60) - timeFrom;
        }
        return totalAmount;
    }

    private static void Main() {
        Console.WriteLine( Solver( Console.In ) );
    }
}