Problem: Polycarpus has a hobby — he develops an unusual social network. His work is almost completed, and there is only one more module to implement — the module which determines friends. Oh yes, in this social network one won't have to add friends manually! Pairs of friends are deduced in the following way. Let's assume that user A sent user B a message at time t1, and user B sent user A a message at time t2. If 0 < t2 - t1 ≤ d, then user B's message was an answer to user A's one. Users A and B are considered to be friends if A answered at least one B's message or B answered at least one A's message.

You are given the log of messages in chronological order and a number d. Find all pairs of users who will be considered to be friends.

Input

The first line of the input contains two integers n and d (1 ≤ n, d ≤ 1000). The next n lines contain the messages log. The i-th line contains one line of the log formatted as "Ai Bi ti" (without the quotes), which means that user Ai sent a message to user Bi at time ti (1 ≤ i ≤ n). Ai and Bi are non-empty strings at most 20 characters long, consisting of lowercase letters ('a' ... 'z'), and ti is an integer (0 ≤ ti ≤ 10000). It is guaranteed that the lines are given in non-decreasing order of ti's and that no user sent a message to himself. The elements in the lines are separated by single spaces.

Output

In the first line print integer k — the number of pairs of friends. In the next k lines print pairs of friends as "Ai Bi" (without the quotes). You can print users in pairs and the pairs themselves in any order. Each pair must be printed exactly once.

Examples

Input

4 1
vasya petya 1
petya vasya 2
anya ivan 2
ivan anya 4


Output

1
petya vasya


Input

1 1000
a b 0


Output

0

Note

In the first sample test case Vasya and Petya are friends because their messages' sending times are one second apart. Anya and Ivan are not, because their messages' sending times differ by more than one second.

Solution (in JAVA):

Solution:

import com.sun.org.apache.bcel.internal.generic.AALOAD;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintStream;
import java.util.ArrayList;
import java.util.StringTokenizer;
import java.util.logging.Level;
import java.util.logging.Logger;

public class ProblemA {

    private final BufferedReader in;
    private final PrintStream out;
    private StringTokenizer tok = new StringTokenizer("");
    private String nextLine = null;

    public static void main(String[] args) throws Exception {
        new ProblemA();
    }

    private ProblemA() throws Exception {
        in = new BufferedReader(new InputStreamReader(System.in));
        out = System.out;
        start();
        end();
    }

    private int nextInt() {
        return Integer.parseInt(nextWord());
    }

    private String nextWord() {
        if (tok.hasMoreTokens()) {
            return tok.nextToken();
        } else {
            while (!tok.hasMoreTokens()) {
                try {
                    nextLine = in.readLine();
                    if (nextLine == null) {
                        return null;
                    } else {
                        tok = new StringTokenizer(nextLine);
                    }
                } catch (IOException ex) {
                    Logger.getLogger(ProblemA.class.getName()).log(Level.SEVERE, null, ex);
                }
            }
            return tok.nextToken();
        }
    }

    private void start() {
        int n = nextInt();
        int d = nextInt();
        User[] users = new User[n];
        int nextU = 0;
        for (int i = 0; i < n; i++) {
            String n1 = nextWord();
            String n2 = nextWord();
            int t = nextInt();
            int hash1 = n1.hashCode();
            Message mes = new Message(n1, n2, t);
            for (int j = 0; j < nextU; j++) {
                if (users[j].hash == hash1) {
                    users[j].me.add(mes);
                    mes = null;
                    break;
                }
            }
            if (mes != null) {
                users[nextU] = new User(n1);
                users[nextU].me.add(mes);
                nextU++;
            }
        }

        boolean[][] friends = new boolean[nextU][nextU];
        int res = 0;
        for (int i = 0; i < nextU; i++) {
            for (Message me : users[i].me) {
                for (int j = 0; j < nextU; j++) {
                    if (users[j].hash == me.hash2) {
                        for (Message me2 : users[j].me) {
                            if (me2.hash2 == me.hash1 && (me2.t - me.t > 0) && (me2.t - me.t <= d)) {
                                if (!friends[i][j]) {
                                    res++;
                                }
                                friends[i][j] = true;
                                friends[j][i] = true;
                                break;
                            }
                        }
                    }
                }
            }
        }
        out.println(res);
        for (int i = 0; i < nextU; i++) {
            for (int j = i + 1; j < nextU; j++) {
                if (friends[i][j]) {
                    out.println(users[i].name + " " + users[j].name);
                }
            }
        }
    }

    class User {

        String name;
        int hash;
        ArrayList<Message> me;

        public User(String name) {
            this.name = name;
            this.hash = name.hashCode();
            me = new ArrayList<Message>();
        }
    }

    class Message {

        String name1;
        String name2;
        int hash1;
        int hash2;
        int t;

        public Message(String name1, String name2, int t) {
            this.name1 = name1;
            this.name2 = name2;
            this.hash1 = name1.hashCode();
            this.hash2 = name2.hashCode();
            this.t = t;
        }
    }

    private void end() {
        out.close();
    }
}