This is a harder version of the problem. In this version, n ≤ 50 000.

There are n distinct points in three-dimensional space numbered from 1 to n. The i-th point has coordinates (x_i, y_i, z_i). The number of points n is even.

You'd like to remove all n points using a sequence of n/2 snaps. In one snap, you can remove any two points a and b that have not been removed yet and form a perfectly balanced pair. A pair of points a and b is perfectly balanced if no other point c (that has not been removed yet) lies within the axis-aligned minimum bounding box of points a and b.

Formally, point c lies within the axis-aligned minimum bounding box of points a and b if and only if min(x_a, x_b) ≤ x_c ≤ max(x_a, x_b), min(y_a, y_b) ≤ y_c ≤ max(y_a, y_b), and min(z_a, z_b) ≤ z_c ≤ max(z_a, z_b). Note that the bounding box might be degenerate. 

Find a way to remove all points in n/2 snaps.

Input

The first line contains a single integer n (2 ≤ n ≤ 50 000; n is even), denoting the number of points.

Each of the next n lines contains three integers x_i, y_i, z_i (-10^8 ≤ x_i, y_i, z_i ≤ 10^8), denoting the coordinates of the i-th point.

No two points coincide.

Output

Output n/2 pairs of integers a_i, b_i (1 ≤ a_i, b_i ≤ n), denoting the indices of points removed on snap i. Every integer between 1 and n, inclusive, must appear in your output exactly once.

We can show that it is always possible to remove all points. If there are many solutions, output any of them.

Examples

Input


6
3 1 0
0 3 0
2 2 0
1 0 0
1 3 0
0 1 0


Output


3 6
5 1
2 4


Input


8
0 1 1
1 0 1
1 1 0
1 1 1
2 2 2
3 2 2
2 3 2
2 2 3


Output


4 5
1 6
2 7
3 8

Note

In the first example, here is what points and their corresponding bounding boxes look like (drawn in two dimensions for simplicity, as all points lie on z = 0 plane). Note that order of removing matters: for example, points 5 and 1 don't form a perfectly balanced pair initially, but they do after point 3 is removed. 

<image>

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.StringTokenizer;
import java.util.function.Function;
import java.util.stream.Collectors;

public class P1237C {

    static boolean multipleIndependent = false;
    static int shift = (int) 1e8;

    void run() {
        int n = in.nextInt();
        List<int[]> points = new ArrayList<>(n);
        for (int i = 0; i < n; i++) {
            points.add(new int[]{
                in.nextInt() + shift,
                in.nextInt() + shift,
                in.nextInt() + shift,
                i + 1
            });
        }
        int[][] result = new int[n / 2][2];
        int ri = 0;
        Map<?, List<int[]>> groups;
        groups = points.stream()
                .collect(Collectors.groupingBy(a -> a[0] + a[1] * ((long) 1e10)));
        points.clear();
        for (List<int[]> v : groups.values()) {
            v.sort(Comparator.comparing(a -> a[2]));
            for (int i = 0; i < v.size() - 1; i += 2) {
                result[ri][0] = v.get(i)[3];
                result[ri][1] = v.get(i + 1)[3];
                ri++;
            }
            if (v.size() % 2 == 1) {
                points.add(v.get(v.size() - 1));
            }
        }
        groups = points.stream()
                .collect(Collectors.groupingBy(a -> a[0]));
        points.clear();
        for (List<int[]> v : groups.values()) {
            v.sort(Comparator.comparing(a -> a[1]));
            for (int i = 0; i < v.size() - 1; i += 2) {
                result[ri][0] = v.get(i)[3];
                result[ri][1] = v.get(i + 1)[3];
                ri++;
            }
            if (v.size() % 2 == 1) {
                points.add(v.get(v.size() - 1));
            }
        }
        points.sort(Comparator.comparing(a -> a[0]));
        for (int i = 0; i < points.size() - 1; i += 2) {
            result[ri][0] = points.get(i)[3];
            result[ri][1] = points.get(i + 1)[3];
            ri++;
        }
        for (int[] a : result) {
            out.println(a[0] + " " + a[1]);
        }
    }

    private boolean isNextInBox(List<int[]> map, int i, int j) {
        boolean result = false;
        if (j + 1 < map.size()) {
            int[] a = map.get(i);
            int[] b = map.get(j);
            int[] c = map.get(j + 1);
            result = c[0] >= Math.min(a[0], b[0]) && c[0] <= Math.max(a[0], b[0])
                    && c[1] >= Math.min(a[1], b[1]) && c[1] <= Math.max(a[1], b[1])
                    && c[2] >= Math.min(a[2], b[2]) && c[2] <= Math.max(a[2], b[2]);
        }
        return result;
    }

    /* -----: Template :----- */
    static InputReader in = new InputReader(System.in);
    static PrintWriter out = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)));

    public static void main(String[] args) {
        int q = multipleIndependent ? in.nextInt() : 1;
        while (q-- > 0) {
            new P1237C().run();
        }
        out.flush();
    }

    static class InputReader {

        private final BufferedReader reader;
        private StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            int bufferSize = 32 * 1024;
            reader = new BufferedReader(new InputStreamReader(stream), bufferSize);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

        public long nextLong() {
            return Long.parseLong(next());
        }

        public int[] nextIntArray(int n) {
            int[] arr = new int[n];
            for (int i = 0; i < n; i++) {
                arr[i] = nextInt();
            }
            return arr;
        }

        public <T> T[] nextIntArrayWithFunction(int n, Function<Integer, T> function, Class<T> c) {
            T[] arr = (T[]) Array.newInstance(c, n);
            for (int i = 0; i < n; i++) {
                arr[i] = function.apply(nextInt());
            }
            return arr;
        }

        public long[] nextLongArray(int n) {
            long[] arr = new long[n];
            for (int i = 0; i < n; i++) {
                arr[i] = nextLong();
            }
            return arr;
        }

        public <T> T[] nextLongArrayWithFunction(int n, Function<Long, T> function, Class<T> c) {
            T[] arr = (T[]) Array.newInstance(c, n);
            for (int i = 0; i < n; i++) {
                arr[i] = function.apply(nextLong());
            }
            return arr;
        }

        public int[][] nextIntMap(int n, int m) {
            int[][] map = new int[n][m];
            for (int i = 0; i < n; i++) {
                map[i] = nextIntArray(m);
            }
            return map;
        }

        public long[][] nextLongMap(int n, int m) {
            long[][] map = new long[n][m];
            for (int i = 0; i < n; i++) {
                map[i] = nextLongArray(m);
            }
            return map;
        }

        public char[][] nextCharMap(int n) {
            char[][] map = new char[n][];
            for (int i = 0; i < n; i++) {
                map[i] = next().toCharArray();
            }
            return map;
        }
    }

    static int numLength(long n) {
        int l = 0;
        while (n > 0) {
            n /= 10;
            l++;
        }
        return l;
    }

    static <R> long binarySearch(long lowerBound, long upperBound,
            R value, Function<Long, R> generatorFunction, Comparator<R> comparator) {
        if (lowerBound <= upperBound) {
            long mid = (lowerBound + upperBound) / 2;
            int compare = comparator.compare(generatorFunction.apply(mid), value);
            if (compare == 0) {
                return mid;
            } else if (compare < 0) {
                return binarySearch(mid + 1, upperBound, value, generatorFunction, comparator);
            } else {
                return binarySearch(lowerBound, mid - 1, value, generatorFunction, comparator);
            }
        } else {
            return -1;
        }
    }

    static <T> Integer[] sortSimultaneously(T[] key, Comparator<T> comparator,
            Object[]... moreArrays) {
        int n = key.length;
        for (Object[] array : moreArrays) {
            if (array.length != n) {
                throw new RuntimeException("Arrays must have equals lengths");
            }
        }
        Integer[] indices = new Integer[n];
        for (int i = 0; i < n; i++) {
            indices[i] = i;
        }
        Comparator<Integer> delegatingComparator = (a, b) -> {
            return comparator.compare(key[a], key[b]);
        };
        Arrays.sort(indices, delegatingComparator);
        reorder(indices, key);
        for (Object[] array : moreArrays) {
            reorder(indices, array);
        }
        return indices;
    }

    static void reorder(Integer[] indices, Object[] arr) {
        if (indices.length != arr.length) {
            throw new RuntimeException("Arrays must have equals lengths");
        }
        int n = arr.length;
        Object[] copy = new Object[n];
        for (int i = 0; i < n; i++) {
            copy[i] = arr[indices[i]];
        }
        System.arraycopy(copy, 0, arr, 0, n);
    }

    static int prodMod(int a, int b, int mod) {
        return (int) (((long) a) * b % mod);
    }

    static long prodMod(long a, long b, long mod) {
        long res = 0;
        a %= mod;
        b %= mod;
        while (b > 0) {
            if ((b & 1) > 0) {
                res = (res + a) % mod;
            }
            a = (a << 1) % mod;
            b >>= 1;
        }
        return res;
    }

    static long sumMod(int[] b, long mod) {
        long res = 0;
        for (int i = 0; i < b.length; i++) {
            res = (res + b[i] % mod) % mod;
        }
        return res;
    }

    static long sumMod(long[] a, long mod) {
        long res = 0;
        for (int i = 0; i < a.length; i++) {
            res = (res + a[i] % mod) % mod;
        }
        return res;
    }

    static long sumProdMod(int[] a, long b, long mod) {
        long res = sumMod(a, mod);
        return prodMod(res, b, mod);
    }

    static long sumProdMod(long[] a, long b, long mod) {
        long res = sumMod(a, mod);
        return prodMod(res, b, mod);
    }

    static long sumProdMod(int[] a, int[] b, long mod) {
        if (a.length != b.length) {
            throw new RuntimeException("Arrays must have equals lengths");
        }
        long res = 0;
        for (int i = 0; i < a.length; i++) {
            res = (res + prodMod(a[i], b[i], mod)) % mod;
        }
        return res;
    }

    static long sumProdMod(long[] a, long[] b, long mod) {
        if (a.length != b.length) {
            throw new RuntimeException("Arrays must have equals lengths");
        }
        long res = 0;
        for (int i = 0; i < a.length; i++) {
            res = (res + prodMod(a[i], b[i], mod)) % mod;
        }
        return res;
    }

    static int[] toPrimitive(Integer[] arr) {
        int[] res = new int[arr.length];
        for (int i = 0; i < arr.length; i++) {
            res[i] = arr[i];
        }
        return res;
    }

    static int[][] toPrimitive(Integer[][] arr) {
        int[][] res = new int[arr.length][];
        for (int i = 0; i < arr.length; i++) {
            res[i] = toPrimitive(arr[i]);
        }
        return res;
    }

    static long[] toPrimitive(Long[] arr) {
        long[] res = new long[arr.length];
        for (int i = 0; i < arr.length; i++) {
            res[i] = arr[i];
        }
        return res;
    }

    static long[][] toPrimitive(Long[][] arr) {
        long[][] res = new long[arr.length][];
        for (int i = 0; i < arr.length; i++) {
            res[i] = toPrimitive(arr[i]);
        }
        return res;
    }

    static Integer[] toWrapper(int[] arr) {
        Integer[] res = new Integer[arr.length];
        for (int i = 0; i < arr.length; i++) {
            res[i] = arr[i];
        }
        return res;
    }

    static Integer[][] toWrapper(int[][] arr) {
        Integer[][] res = new Integer[arr.length][];
        for (int i = 0; i < arr.length; i++) {
            res[i] = toWrapper(arr[i]);
        }
        return res;
    }

    static Long[] toWrapper(long[] arr) {
        Long[] res = new Long[arr.length];
        for (int i = 0; i < arr.length; i++) {
            res[i] = arr[i];
        }
        return res;
    }

    static Long[][] toWrapper(long[][] arr) {
        Long[][] res = new Long[arr.length][];
        for (int i = 0; i < arr.length; i++) {
            res[i] = toWrapper(arr[i]);
        }
        return res;
    }
}
