using System;

class Program
{
    static void Main()
    {
        int n = int.Parse(Console.ReadLine());
        int[] H = new int[n];
        int[] M = new int[n];
        int[] h = new int[n];
        int[] m = new int[n];
        for (int i = 0; i < n; i++)
        {
            string[] s = Console.ReadLine().Split();
            H[i] = int.Parse(s[0].Split(':')[0]);
            M[i] = int.Parse(s[0].Split(':')[1]);
            h[i] = int.Parse(s[1].Split(':')[0]);
            m[i] = int.Parse(s[1].Split(':')[1]);
        }

        int sleep = 0;

        for (int i = 0; i < n; i++)
        {
            if (H[i] > h[i]) h[i] += 24;
            sleep += h[i] * 60 + m[i] - H[i] * 60 - M[i];
        }

        Console.WriteLine(sleep);
    }
}