import java.io.*;
import java.util.*;
import java.util.stream.*;

// 処理
class Process {
    private int[] H;
    private int[] M;
    private int[] h;
    private int[] m;

    Process(int[] H, int[] M, int[] h, int[] m) {
        this.H = H;
        this.M = M;
        this.h = h;
        this.m = m;
    }
    
    // 引数で与えられる時刻について、 0 時 0 分 から何分経っているか 
    private int minute(int hour, int minute) {
        return ((hour * 60) + minute);
    }

    int getResult() {
        int sleepTime = 0;
        int sumOfSleepTime = 0;
        
        for(int i = 0; i < H.length; i++) {
            sleepTime = (minute(h[i], m[i]) - minute(H[i], M[i]));
            if(sleepTime < 0) {
                sleepTime += minute(24, 0);
            }

            sumOfSleepTime += sleepTime;
        }
        
        
        return sumOfSleepTime;
    }
}

public class Main {
    public static void main(String[] args) throws IOException {
        var bufferedReader = new BufferedReader(new InputStreamReader(System.in));
        var printWriter    = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)));

        // 入力
        int N = Integer.parseInt(bufferedReader.readLine().trim());
        
        var H = new int[N];
        var M = new int[N];
        var h = new int[N];
        var m = new int[N];
        for(int i = 0; i < N; i++) {
            int[] input = Stream.of(bufferedReader.readLine().trim().split("[: ]+")).mapToInt(Integer::parseInt).toArray();
            H[i] = input[0];
            M[i] = input[1];
            h[i] = input[2];
            m[i] = input[3];
        }

        // 出力
        printWriter.println((new Process(H, M, h, m)).getResult());

        bufferedReader.close();
        printWriter.close();
    }
}