using System;
using System.Collections.Generic;
using System.Text;

public class Program
{
    public void Proc(){
        Reader.IsDebug = false;
        int inputCount = int.Parse(Reader.ReadLine());
        
        int ans = 0;
        for(int i=0; i<inputCount; i++) {
            string[] inpt = Reader.ReadLine().Split(' ');
            DateTime dtFrom = DateTime.Parse(inpt[0]);
            DateTime dtTo = DateTime.Parse(inpt[1]);
            if(dtFrom.CompareTo(dtTo) > 0) {
                dtTo = dtTo.AddDays(1);
            }
            ans += (int)dtTo.Subtract(dtFrom).TotalMinutes;
        }
        Console.WriteLine(ans);
    }
    
    public static void Main(string[] args)
    {
        Program prg = new Program();
        prg.Proc();
    }
}

class Reader
{
    public static bool IsDebug = true;
    
    private static System.IO.StringReader sr;
    
    public static string ReadLine() {
        if(IsDebug) {
            if(sr == null) {
                sr = new System.IO.StringReader(initStr.Trim());
            }
            return sr.ReadLine();
        } else {
            return Console.ReadLine();
        }
    }
    
    public static int[] GetInt(char delimiter = ' ', bool mustTrim = false) {
        string src = ReadLine();
        if(mustTrim) {
            src = src.Trim();
        }
        string[] inpt = src.Split(delimiter);
        int[] ret = new int[inpt.Length];
        for(int i=0; i<inpt.Length; i++) {
            string item = inpt[i];
            if(mustTrim) {
                item = item.Trim();
            }
            ret[i] = int.Parse(item);
        }
        return ret;
    }
    
    private static string initStr = @"

5
22:30 4:30
22:46 4:46
1:17 7:26
0:38 7:0
23:49 7:41


";
}