using System;
using System.Linq;

public class P0070 {
    public static void Main() {
        var n = int.Parse(Console.ReadLine().Trim());
        const int day = 1440;
        int result = 0;
        for(int i=0; i<n; i++) {
            var hmhm = Console.ReadLine().Trim().Split(' ').SelectMany(s => s.Split(":")).Select(int.Parse).ToList();
            var start = hmhm[0] * 60 + hmhm[1];
            var end   = hmhm[2] * 60 + hmhm[3];
            if(end < start) {
                result += day - start + end;
            } else {
                result += end - start;
            }
        }
        Console.WriteLine(result);
    }
}