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 java.io.BufferedReader;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.*;

/**
 * User: artpetroff
 * Date: 09.03.12
 * Time: 12:39
 */
public class _159A {

    public static void main(String[] args) {
        try {
            final BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
            String s = reader.readLine();
            final int n = Integer.parseInt(s.substring(0, s.indexOf(' ')));
            final int d = Integer.parseInt(s.substring(s.indexOf(' ') + 1));
            final Map<Pair<String, String>, List<Integer>> m = new HashMap<Pair<String, String>, List<Integer>>();

            for (int i = 0; i < n; i++) {
                readLine(reader.readLine(), m);
            }
            final List<Pair<String, String>> pairs = getPairs(m, d);
            System.out.println(pairs.size());
            for (final Pair<String, String> pair : pairs) {
                System.out.println(pair.a + " " + pair.b);
            }
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    private static List<Pair<String, String>> getPairs(final Map<Pair<String, String>, List<Integer>> fromMap, final int d) {
        final List<Pair<String, String>> out = new ArrayList<Pair<String, String>>();
        for (final Map.Entry<Pair<String, String>, List<Integer>> entry : new HashSet<Map.Entry<Pair<String, String>, List<Integer>>>(fromMap.entrySet())) {
            final Pair<String, String> pair = entry.getKey();
            final List<Integer> l1 = entry.getValue();
            final List<Integer> l2 = fromMap.remove(Pair.of(pair.b, pair.a));
            fromMap.remove(pair);
            if (l1 != null && l2 != null) {
                if (wasReply(l1,l2,d) || wasReply(l2,l1,d)) {
                    out.add(pair);
                }
            }
        }
        return out;
    }

    public static boolean wasReply(final List<Integer> l1, final List<Integer> l2, final int d) {
        if (l1.isEmpty() || l2.isEmpty()) {
            return false;
        }
        final Iterator<Integer> i1 = l1.iterator();
        final Iterator<Integer> i2 = l2.iterator();
        int a1 = Integer.MIN_VALUE;
        int a2 = i2.next();
        while (i1.hasNext()) {
            a1 = i1.next();
            if (a1 > a2 && a1 <= a2 + d) {
                return true;
            }
            while (a1 > a2 + d && i2.hasNext()) {
                a2 = i2.next();
            }
            if (a1 > a2 && a1 <= a2 + d) {
                return true;
            }
        }

        return false;
    }

    private static void readLine(final String s, final Map<Pair<String, String>, List<Integer>> fromMap) {
        final Scanner scanner = new Scanner(new ByteArrayInputStream(s.getBytes()));
        final String from = scanner.next();
        final String to = scanner.next();
        final Integer time = scanner.nextInt();
        addToMap(fromMap, from, to, time);
    }

    private static void addToMap(final Map<Pair<String, String>, List<Integer>> m, final String a, final String b, final Integer time) {
        final Pair<String, String> pair = Pair.of(a, b);
        List<Integer> list = m.get(pair);
        if (list == null) {
            list = new ArrayList<Integer>();
            m.put(pair, list);
        }
        list.add(time);
    }

    static class Pair<A,B> {
        final A a;
        final B b;

        Pair(final A a, final B b) {
            this.a = a;
            this.b = b;
        }

        @Override
        public boolean equals(final Object o) {
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;

            final Pair pair = (Pair) o;

            if (!a.equals(pair.a)) return false;
            if (!b.equals(pair.b)) return false;

            return true;
        }

        @Override
        public int hashCode() {
            int result = a.hashCode();
            result = 31 * result + b.hashCode();
            return result;
        }

        public static <A,B> Pair<A,B> of(final A a, final B b) {
            return new Pair<A, B>(a, b);
        }

        @Override
        public String toString() {
            return "[" + a + ", " + b + ']';
        }
    }

}