This is a harder version of the problem. In this version, $n \le 50\,000$.

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 $\frac{n}{2}$ 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 $\min(x_a, x_b) \le x_c \le \max(x_a, x_b)$, $\min(y_a, y_b) \le y_c \le \max(y_a, y_b)$, and $\min(z_a, z_b) \le z_c \le \max(z_a, z_b)$. Note that the bounding box might be degenerate. 

Find a way to remove all points in $\frac{n}{2}$ snaps.


-----Input-----

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

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

No two points coincide.


-----Output-----

Output $\frac{n}{2}$ pairs of integers $a_i, b_i$ ($1 \le a_i, b_i \le n$), 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]

Difficulty: HARD
Tags: Constructive algorithms

Sorting

Implementation

Greedy algorithms

Divide and conquer
Skill types: Sorting

Greedy algorithms

Starter code:

Solutions:
n = int(input())
sentinel = [(10 ** 9, 10 ** 9, 10 ** 9)]
points = sorted((tuple(map(int, input().split())) + (i,) for i in range(1, n + 1))) + sentinel
ans = []
rem = []
i = 0
while i < n:
	if points[i][:2] == points[i + 1][:2]:
		ans.append(f'{points[i][-1]} {points[i + 1][-1]}')
		i += 2
	else:
		rem.append(i)
		i += 1
rem += [n]
rem2 = []
n = len(rem)
i = 0
while i < n - 1:
	if points[rem[i]][0] == points[rem[i + 1]][0]:
		ans.append(f'{points[rem[i]][-1]} {points[rem[i + 1]][-1]}')
		i += 2
	else:
		rem2.append(points[rem[i]][-1])
		i += 1
print(*ans, sep='\n')
for i in range(0, len(rem2), 2):
	print(rem2[i], rem2[i + 1])


from collections import OrderedDict

def SortPoint(p, ids, k, D):
	if k == D:
		return ids[0]
	maps = OrderedDict()
	for i in ids:
		if p[i][k] not in maps:
			maps[p[i][k]] = []
		maps[p[i][k]].append(i)
	a = []
	for i in sorted(maps.keys()):
		cnt = SortPoint(p, maps[i], k + 1, D)
		if cnt != -1:
			a.append(cnt)
	for i in range(0, len(a), 2):
		if i + 1 < len(a):
			print(a[i] + 1, a[i + 1] + 1)
	return -1 if len(a) % 2 == 0 else a[-1]

def solver():
	n = int(input())
	p = []
	ids = [i for i in range(n)]
	for i in range(n):
		point = list(map(int, input().split()))
		p.append(point)
	SortPoint(p, ids, 0, 3)

def main():
	while 1:
		try:
			solver()
		except EOFError:
			break

def __starting_point():
	main()
__starting_point()


import os
import sys
from io import BytesIO, IOBase
from collections import defaultdict

def main():
	n = int(input())
	b = defaultdict(list)
	for i in range(n):
		(x, y, z) = map(int, input().split())
		b[z].append((x, y, i + 1))
	dd = []
	ans = []
	for i in sorted(b.keys()):
		c = defaultdict(list)
		for j in b[i]:
			c[j[1]].append((j[0], j[2]))
		d = []
		for j in sorted(c.keys()):
			z = c[j]
			z.sort(key=lambda x: x[0])
			if len(z) % 2:
				d.append(z.pop()[-1])
			for k in range(0, len(z), 2):
				ans.append((z[k][-1], z[k + 1][-1]))
		if len(d) % 2:
			dd.append(d.pop())
		for j in range(0, len(d), 2):
			ans.append((d[j], d[j + 1]))
	for i in range(0, len(dd), 2):
		ans.append((dd[i], dd[i + 1]))
	for i in ans:
		print(*i)
BUFSIZE = 8192

class FastIO(IOBase):
	newlines = 0

	def __init__(self, file):
		self._fd = file.fileno()
		self.buffer = BytesIO()
		self.writable = 'x' in file.mode or 'r' not in file.mode
		self.write = self.buffer.write if self.writable else None

	def read(self):
		while True:
			b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
			if not b:
				break
			ptr = self.buffer.tell()
			(self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr))
		self.newlines = 0
		return self.buffer.read()

	def readline(self):
		while self.newlines == 0:
			b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
			self.newlines = b.count(b'\n') + (not b)
			ptr = self.buffer.tell()
			(self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr))
		self.newlines -= 1
		return self.buffer.readline()

	def flush(self):
		if self.writable:
			os.write(self._fd, self.buffer.getvalue())
			(self.buffer.truncate(0), self.buffer.seek(0))

class IOWrapper(IOBase):

	def __init__(self, file):
		self.buffer = FastIO(file)
		self.flush = self.buffer.flush
		self.writable = self.buffer.writable
		self.write = lambda s: self.buffer.write(s.encode('ascii'))
		self.read = lambda : self.buffer.read().decode('ascii')
		self.readline = lambda : self.buffer.readline().decode('ascii')
(sys.stdin, sys.stdout) = (IOWrapper(sys.stdin), IOWrapper(sys.stdout))
input = lambda : sys.stdin.readline().rstrip('\r\n')
main()


n = int(input())
p = [list(map(int, input().split())) + [i] for i in range(n)] + [[10 ** 9, 10 ** 9, 10 ** 9]]
p.sort(key=lambda x: tuple(x[:-1]))
rem = []
i = 0
while i < n:
	if p[i][:2] == p[i + 1][:2]:
		print(p[i][-1] + 1, p[i + 1][-1] + 1)
		i += 2
	else:
		rem.append(p[i])
		i += 1
rem += [p[n]]
rem2 = []
n = len(rem)
i = 0
while i < n - 1:
	if rem[i][0] == rem[i + 1][0]:
		print(rem[i][-1] + 1, rem[i + 1][-1] + 1)
		i += 2
	else:
		rem2.append(rem[i])
		i += 1
for i in range(0, len(rem2), 2):
	print(rem2[i][-1] + 1, rem2[i + 1][-1] + 1)


n = int(input())
points = []
for i in range(n):
	points.append(list(map(int, input().split())))
	points[i].append(i + 1)
points.sort()
rem = []
i = 0
while i < len(points):
	if i < len(points) - 1 and points[i][:2] == points[i + 1][:2]:
		print(points[i][3], points[i + 1][3])
		i += 2
	else:
		rem.append(points[i])
		i += 1
points = list(rem)
rem = []
i = 0
while i < len(points):
	if i < len(points) - 1 and points[i][0] == points[i + 1][0]:
		print(points[i][3], points[i + 1][3])
		i += 2
	else:
		rem.append(points[i])
		i += 1
points = list(rem)
rem = []
i = 0
while i < len(points) - 1:
	print(points[i][3], points[i + 1][3])
	i += 2


from math import *
import sys
input = sys.stdin.readline
global flag

def inp():
	return int(input())

def st():
	return input().rstrip('\n')

def lis():
	return list(map(int, input().split()))

def ma1():
	return map(int, input().split())
t = 1
while t:
	t -= 1
	n = inp()
	r = []
	di = {}
	for i in range(n):
		a = lis()
		a += [i]
		r.append(a)
		try:
			di[a[-2]].append(a)
		except:
			di[a[-2]] = [a]
	ydi = {}
	extra = []
	for i in di.keys():
		extray = []
		for j in di[i]:
			try:
				ydi[j[-3]].append(j)
			except:
				ydi[j[-3]] = [j]
		for j in ydi.keys():
			ydi[j].sort()
		for j in ydi.keys():
			for k in range(0, len(ydi[j]) - len(ydi[j]) % 2, 2):
				print(ydi[j][k][-1] + 1, ydi[j][k + 1][-1] + 1)
			if len(ydi[j]) % 2:
				has = ydi[j][-1]
				has1 = [has[-3], has[-4], has[-2], has[-1]]
				extray.append(has1)
		extray.sort()
		for j in range(0, len(extray) - len(extray) % 2, 2):
			print(extray[j][-1] + 1, extray[j + 1][-1] + 1)
		if len(extray) % 2:
			has = [extray[-1][-2], extray[-1][-3], extray[-1][-4], extray[-1][-1]]
			extra.append(has)
		ydi = {}
		extray = []
	extra.sort()
	for i in range(0, len(extra), 2):
		print(extra[i][-1] + 1, extra[i + 1][-1] + 1)


n = int(input())
coordinates = []
for i in range(n):
	coordinates.append([int(i) for i in input().split()])
	coordinates[i].append(i + 1)
coordinates.sort()
remaining = []
i = 0
while i < len(coordinates):
	if i < len(coordinates) - 1 and coordinates[i][:2] == coordinates[i + 1][:2]:
		print(coordinates[i][3], coordinates[i + 1][3])
		i += 2
	else:
		remaining.append(coordinates[i])
		i += 1
coordinates = list(remaining)
remaining = []
i = 0
while i < len(coordinates):
	if i < len(coordinates) - 1 and coordinates[i][0] == coordinates[i + 1][0]:
		print(coordinates[i][3], coordinates[i + 1][3])
		i += 2
	else:
		remaining.append(coordinates[i])
		i += 1
coordinates = list(remaining)
for i in range(int(len(coordinates)) // 2):
	print(coordinates[2 * i][3], coordinates[2 * i + 1][3])


import math
import random
import heapq, bisect
import sys
from collections import deque, defaultdict
from fractions import Fraction
import sys
import threading
from collections import defaultdict
threading.stack_size(10 ** 8)
mod = 10 ** 9 + 7
mod1 = 998244353
import os
import sys
from io import BytesIO, IOBase
sys.setrecursionlimit(300000)
BUFSIZE = 8192

class FastIO(IOBase):
	newlines = 0

	def __init__(self, file):
		self._fd = file.fileno()
		self.buffer = BytesIO()
		self.writable = 'x' in file.mode or 'r' not in file.mode
		self.write = self.buffer.write if self.writable else None

	def read(self):
		while True:
			b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
			if not b:
				break
			ptr = self.buffer.tell()
			(self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr))
		self.newlines = 0
		return self.buffer.read()

	def readline(self):
		while self.newlines == 0:
			b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
			self.newlines = b.count(b'\n') + (not b)
			ptr = self.buffer.tell()
			(self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr))
		self.newlines -= 1
		return self.buffer.readline()

	def flush(self):
		if self.writable:
			os.write(self._fd, self.buffer.getvalue())
			(self.buffer.truncate(0), self.buffer.seek(0))

class IOWrapper(IOBase):

	def __init__(self, file):
		self.buffer = FastIO(file)
		self.flush = self.buffer.flush
		self.writable = self.buffer.writable
		self.write = lambda s: self.buffer.write(s.encode('ascii'))
		self.read = lambda : self.buffer.read().decode('ascii')
		self.readline = lambda : self.buffer.readline().decode('ascii')
(sys.stdin, sys.stdout) = (IOWrapper(sys.stdin), IOWrapper(sys.stdout))
input = lambda : sys.stdin.readline().rstrip('\r\n')

class TreeNode:

	def __init__(self, k, v):
		self.key = k
		self.value = v
		self.left = None
		self.right = None
		self.parent = None
		self.height = 1
		self.num_left = 1
		self.num_total = 1

class AvlTree:

	def __init__(self):
		self._tree = None

	def add(self, k, v):
		if not self._tree:
			self._tree = TreeNode(k, v)
			return
		node = self._add(k, v)
		if node:
			self._rebalance(node)

	def _add(self, k, v):
		node = self._tree
		while node:
			if k < node.key:
				if node.left:
					node = node.left
				else:
					node.left = TreeNode(k, v)
					node.left.parent = node
					return node.left
			elif node.key < k:
				if node.right:
					node = node.right
				else:
					node.right = TreeNode(k, v)
					node.right.parent = node
					return node.right
			else:
				node.value = v
				return

	@staticmethod
	def get_height(x):
		return x.height if x else 0

	@staticmethod
	def get_num_total(x):
		return x.num_total if x else 0

	def _rebalance(self, node):
		n = node
		while n:
			lh = self.get_height(n.left)
			rh = self.get_height(n.right)
			n.height = max(lh, rh) + 1
			balance_factor = lh - rh
			n.num_total = 1 + self.get_num_total(n.left) + self.get_num_total(n.right)
			n.num_left = 1 + self.get_num_total(n.left)
			if balance_factor > 1:
				if self.get_height(n.left.left) < self.get_height(n.left.right):
					self._rotate_left(n.left)
				self._rotate_right(n)
			elif balance_factor < -1:
				if self.get_height(n.right.right) < self.get_height(n.right.left):
					self._rotate_right(n.right)
				self._rotate_left(n)
			else:
				n = n.parent

	def _remove_one(self, node):
		replacement = node.left or node.right
		if node.parent:
			if AvlTree._is_left(node):
				node.parent.left = replacement
			else:
				node.parent.right = replacement
			replacement.parent = node.parent
			node.parent = None
		else:
			self._tree = replacement
			replacement.parent = None
		node.left = None
		node.right = None
		node.parent = None
		self._rebalance(replacement)

	def _remove_leaf(self, node):
		if node.parent:
			if AvlTree._is_left(node):
				node.parent.left = None
			else:
				node.parent.right = None
			self._rebalance(node.parent)
		else:
			self._tree = None
		node.parent = None
		node.left = None
		node.right = None

	def remove(self, k):
		node = self._get_node(k)
		if not node:
			return
		if AvlTree._is_leaf(node):
			self._remove_leaf(node)
			return
		if node.left and node.right:
			nxt = AvlTree._get_next(node)
			node.key = nxt.key
			node.value = nxt.value
			if self._is_leaf(nxt):
				self._remove_leaf(nxt)
			else:
				self._remove_one(nxt)
			self._rebalance(node)
		else:
			self._remove_one(node)

	def get(self, k):
		node = self._get_node(k)
		return node.value if node else -1

	def _get_node(self, k):
		if not self._tree:
			return None
		node = self._tree
		while node:
			if k < node.key:
				node = node.left
			elif node.key < k:
				node = node.right
			else:
				return node
		return None

	def get_at(self, pos):
		x = pos + 1
		node = self._tree
		while node:
			if x < node.num_left:
				node = node.left
			elif node.num_left < x:
				x -= node.num_left
				node = node.right
			else:
				return (node.key, node.value)
		raise IndexError('Out of ranges')

	@staticmethod
	def _is_left(node):
		return node.parent.left and node.parent.left == node

	@staticmethod
	def _is_leaf(node):
		return node.left is None and node.right is None

	def _rotate_right(self, node):
		if not node.parent:
			self._tree = node.left
			node.left.parent = None
		elif AvlTree._is_left(node):
			node.parent.left = node.left
			node.left.parent = node.parent
		else:
			node.parent.right = node.left
			node.left.parent = node.parent
		bk = node.left.right
		node.left.right = node
		node.parent = node.left
		node.left = bk
		if bk:
			bk.parent = node
		node.height = max(self.get_height(node.left), self.get_height(node.right)) + 1
		node.num_total = 1 + self.get_num_total(node.left) + self.get_num_total(node.right)
		node.num_left = 1 + self.get_num_total(node.left)

	def _rotate_left(self, node):
		if not node.parent:
			self._tree = node.right
			node.right.parent = None
		elif AvlTree._is_left(node):
			node.parent.left = node.right
			node.right.parent = node.parent
		else:
			node.parent.right = node.right
			node.right.parent = node.parent
		bk = node.right.left
		node.right.left = node
		node.parent = node.right
		node.right = bk
		if bk:
			bk.parent = node
		node.height = max(self.get_height(node.left), self.get_height(node.right)) + 1
		node.num_total = 1 + self.get_num_total(node.left) + self.get_num_total(node.right)
		node.num_left = 1 + self.get_num_total(node.left)

	@staticmethod
	def _get_next(node):
		if not node.right:
			return node.parent
		n = node.right
		while n.left:
			n = n.left
		return n

class SegmentTree1:

	def __init__(self, data, default=2 ** 51, func=lambda a, b: a & b):
		self._default = default
		self._func = func
		self._len = len(data)
		self._size = _size = 1 << (self._len - 1).bit_length()
		self.data = [default] * (2 * _size)
		self.data[_size:_size + self._len] = data
		for i in reversed(range(_size)):
			self.data[i] = func(self.data[i + i], self.data[i + i + 1])

	def __delitem__(self, idx):
		self[idx] = self._default

	def __getitem__(self, idx):
		return self.data[idx + self._size]

	def __setitem__(self, idx, value):
		idx += self._size
		self.data[idx] = value
		idx >>= 1
		while idx:
			self.data[idx] = self._func(self.data[2 * idx], self.data[2 * idx + 1])
			idx >>= 1

	def __len__(self):
		return self._len

	def query(self, start, stop):
		if start == stop:
			return self.__getitem__(start)
		stop += 1
		start += self._size
		stop += self._size
		res = self._default
		while start < stop:
			if start & 1:
				res = self._func(res, self.data[start])
				start += 1
			if stop & 1:
				stop -= 1
				res = self._func(res, self.data[stop])
			start >>= 1
			stop >>= 1
		return res

	def __repr__(self):
		return 'SegmentTree({0})'.format(self.data)

class SegmentTree:

	def __init__(self, data, default=0, func=lambda a, b: a + b):
		self._default = default
		self._func = func
		self._len = len(data)
		self._size = _size = 1 << (self._len - 1).bit_length()
		self.data = [default] * (2 * _size)
		self.data[_size:_size + self._len] = data
		for i in reversed(range(_size)):
			self.data[i] = func(self.data[i + i], self.data[i + i + 1])

	def __delitem__(self, idx):
		self[idx] = self._default

	def __getitem__(self, idx):
		return self.data[idx + self._size]

	def __setitem__(self, idx, value):
		idx += self._size
		self.data[idx] = value
		idx >>= 1
		while idx:
			self.data[idx] = self._func(self.data[2 * idx], self.data[2 * idx + 1])
			idx >>= 1

	def __len__(self):
		return self._len

	def query(self, start, stop):
		if start == stop:
			return self.__getitem__(start)
		stop += 1
		start += self._size
		stop += self._size
		res = self._default
		while start < stop:
			if start & 1:
				res = self._func(res, self.data[start])
				start += 1
			if stop & 1:
				stop -= 1
				res = self._func(res, self.data[stop])
			start >>= 1
			stop >>= 1
		return res

	def __repr__(self):
		return 'SegmentTree({0})'.format(self.data)

class Factorial:

	def __init__(self, MOD):
		self.MOD = MOD
		self.factorials = [1, 1]
		self.invModulos = [0, 1]
		self.invFactorial_ = [1, 1]

	def calc(self, n):
		if n <= -1:
			print('Invalid argument to calculate n!')
			print('n must be non-negative value. But the argument was ' + str(n))
			exit()
		if n < len(self.factorials):
			return self.factorials[n]
		nextArr = [0] * (n + 1 - len(self.factorials))
		initialI = len(self.factorials)
		prev = self.factorials[-1]
		m = self.MOD
		for i in range(initialI, n + 1):
			prev = nextArr[i - initialI] = prev * i % m
		self.factorials += nextArr
		return self.factorials[n]

	def inv(self, n):
		if n <= -1:
			print('Invalid argument to calculate n^(-1)')
			print('n must be non-negative value. But the argument was ' + str(n))
			exit()
		p = self.MOD
		pi = n % p
		if pi < len(self.invModulos):
			return self.invModulos[pi]
		nextArr = [0] * (n + 1 - len(self.invModulos))
		initialI = len(self.invModulos)
		for i in range(initialI, min(p, n + 1)):
			next = -self.invModulos[p % i] * (p // i) % p
			self.invModulos.append(next)
		return self.invModulos[pi]

	def invFactorial(self, n):
		if n <= -1:
			print('Invalid argument to calculate (n^(-1))!')
			print('n must be non-negative value. But the argument was ' + str(n))
			exit()
		if n < len(self.invFactorial_):
			return self.invFactorial_[n]
		self.inv(n)
		nextArr = [0] * (n + 1 - len(self.invFactorial_))
		initialI = len(self.invFactorial_)
		prev = self.invFactorial_[-1]
		p = self.MOD
		for i in range(initialI, n + 1):
			prev = nextArr[i - initialI] = prev * self.invModulos[i % p] % p
		self.invFactorial_ += nextArr
		return self.invFactorial_[n]

class Combination:

	def __init__(self, MOD):
		self.MOD = MOD
		self.factorial = Factorial(MOD)

	def ncr(self, n, k):
		if k < 0 or n < k:
			return 0
		k = min(k, n - k)
		f = self.factorial
		return f.calc(n) * f.invFactorial(max(n - k, k)) * f.invFactorial(min(k, n - k)) % self.MOD

def powm(a, n, m):
	if a == 1 or n == 0:
		return 1
	if n % 2 == 0:
		s = powm(a, n // 2, m)
		return s * s % m
	else:
		return a * powm(a, n - 1, m) % m

def sort_list(list1, list2):
	zipped_pairs = zip(list2, list1)
	z = [x for (_, x) in sorted(zipped_pairs)]
	return z

def product(l):
	por = 1
	for i in range(len(l)):
		por *= l[i]
	return por

def binarySearchCount(arr, n, key):
	left = 0
	right = n - 1
	count = 0
	while left <= right:
		mid = int((right + left) / 2)
		if arr[mid] < key:
			count = mid + 1
			left = mid + 1
		else:
			right = mid - 1
	return count

def countdig(n):
	c = 0
	while n > 0:
		n //= 10
		c += 1
	return c

def binary(x, length):
	y = bin(x)[2:]
	return y if len(y) >= length else '0' * (length - len(y)) + y

def countGreater(arr, n, k):
	l = 0
	r = n - 1
	leftGreater = n
	while l <= r:
		m = int(l + (r - l) / 2)
		if arr[m] >= k:
			leftGreater = m
			r = m - 1
		else:
			l = m + 1
	return n - leftGreater
n = int(input())
d = defaultdict(list)

def solve(e):
	e.sort()
	for i in range(len(e) // 2):
		print(e[2 * i][3], e[2 * i + 1][3])
	if len(e) % 2 == 1:
		return e[-1]
	else:
		return -1

def solve2(l):
	de = defaultdict(list)
	for i in range(len(l)):
		de[l[i][1]].append((l[i][0], l[i][1], l[i][2], l[i][3]))
	e = []
	for i in de:
		r = solve(de[i])
		if r != -1:
			e.append(r)
	e.sort()
	for i in range(len(e) // 2):
		print(e[2 * i][3], e[2 * i + 1][3])
	if len(e) % 2 == 1:
		return e[-1]
	else:
		return -1
for i in range(n):
	(a, b, c) = map(int, input().split())
	d[a].append((a, b, c, i + 1))
e = []
for i in d:
	r = solve2(d[i])
	if r != -1:
		e.append(r)
e.sort()
for i in range(len(e) // 2):
	print(e[2 * i][3], e[2 * i + 1][3])


n = int(input())
dot = []
for i in range(n):
	(x, y, z) = map(int, input().split())
	dot.append([x, y, z, i + 1])
dot.sort(key=lambda x: (x[2], x[0], x[1]))
m = {}
for i in range(n):
	if dot[i][2] not in m:
		m[dot[i][2]] = [dot[i]]
	else:
		m[dot[i][2]].append(dot[i])
new_m = []
for key in m:
	pl = m[key]
	g = {}
	for i in range(len(pl)):
		if pl[i][0] not in g:
			g[pl[i][0]] = [pl[i]]
		else:
			g[pl[i][0]].append(pl[i])
	e = []
	for gkey in g:
		for i in range(0, len(g[gkey]) - 1, 2):
			print(g[gkey][i][-1], g[gkey][i + 1][-1])
		if len(g[gkey]) % 2 == 1:
			e.append(g[gkey][-1])
	for i in range(0, len(e) - 1, 2):
		print(e[i][-1], e[i + 1][-1])
	if len(e) % 2 == 1:
		new_m.append(e[-1])
for i in range(0, len(new_m), 2):
	print(new_m[i][-1], new_m[i + 1][-1])


from collections import deque
n = int(input())
points = [0] * n
planes = {}
other = []
for i in range(n):
	(x, y, z) = map(float, input().split())
	points[i] = (x, y, z, i + 1)
	planes[z] = []
for i in range(n):
	(x, y, z, index) = points[i]
	planes[points[i][2]].append((x, y, z, index))
for i in planes.keys():
	now = deque(sorted(planes[i], key=lambda x: (x[0], x[1])))
	while len(now) >= 3:
		first = now.popleft()
		second = now.popleft()
		third = now.popleft()
		if second[0] == third[0]:
			while second[0] == third[0] and len(now) >= 3:
				print(second[3], third[3])
				second = now.popleft()
				third = now.popleft()
			if second[0] == third[0]:
				print(second[3], third[3])
				now.appendleft(first)
			else:
				now.appendleft(third)
				print(first[3], second[3])
		else:
			now.appendleft(third)
			print(first[3], second[3])
	if len(now) == 2:
		first = now.popleft()
		second = now.popleft()
		print(first[3], second[3])
	else:
		first = now.popleft()
		other.append(first)
other.sort(key=lambda x: x[2])
for i in range(len(other) // 2):
	print(other[2 * i][3], other[2 * i + 1][3])


n = int(input())
arr = []
for i in range(n):
	(a, b, c) = map(int, input().split())
	arr.append([a, b, c] + [i + 1])
arr.sort()
ans = []
for i in range(2, -1, -1):
	st = []
	for x in arr:
		if st and all((st[-1][itr] <= x[itr] for itr in range(i + 1))):
			ans.append((st.pop()[-1], x[-1]))
		else:
			st.append(x)
	arr = st
for i in ans:
	print(i[0], i[1])


n = int(input())
coord = []
for i in range(n):
	coord.append(tuple(list(map(int, input().split())) + [i + 1]))
coord.sort()

def odind(l):
	l.sort()
	for i in range(len(l) // 2):
		print(l[2 * i][-1], l[2 * i + 1][-1])
	if len(l) % 2 == 0:
		return []
	return l[-1]

def dvad(l):
	cx = {}
	ans1 = []
	for (x, y, n) in l:
		if x in cx:
			cx[x].append([y, n])
		else:
			cx[x] = [[y, n]]
	for (x, j) in cx.items():
		v = odind(j)
		if len(v) != 0:
			ans1.append(tuple([x] + v))
	ans1.sort()
	for i in range(len(ans1) // 2):
		print(ans1[2 * i][-1], ans1[2 * i + 1][-1])
	if len(ans1) % 2 == 0:
		return []
	return ans1[-1]

def trid(l):
	cx = {}
	ans1 = []
	for (x, y, z, n) in l:
		if x in cx:
			cx[x].append((y, z, n))
		else:
			cx[x] = [(y, z, n)]
	for (x, j) in cx.items():
		v = list(dvad(j))
		if len(v) != 0:
			ans1.append(tuple([x] + v))
	ans1.sort()
	for i in range(len(ans1) // 2):
		print(ans1[2 * i][-1], ans1[2 * i + 1][-1])
trid(coord)


import sys
n = -1
data = []
for line in sys.stdin:
	if n == -1:
		n = int(line)
		continue
	data.append(tuple([int(i) for i in line.split()]))
	if len(data) == n:
		break
data = list(zip(data, list(range(1, n + 1))))
data.sort()
data2 = []
removedLast = False
for i in range(n):
	if removedLast:
		removedLast = False
		continue
	if i + 1 < n and data[i][0][0] == data[i + 1][0][0] and (data[i][0][1] == data[i + 1][0][1]):
		print('%d %d' % (data[i][1], data[i + 1][1]))
		removedLast = True
	else:
		data2.append(data[i])
data3 = []
removedLast = False
for i in range(len(data2)):
	if removedLast:
		removedLast = False
		continue
	if i + 1 < len(data2) and data2[i][0][0] == data2[i + 1][0][0]:
		print('%d %d' % (data2[i][1], data2[i + 1][1]))
		removedLast = True
	else:
		data3.append(data2[i])
for i in range(0, len(data3), 2):
	print('%d %d' % (data3[i][1], data3[i + 1][1]))


import sys
input = lambda : sys.stdin.readline().rstrip()
N = int(input())
D = {}
ans = []
for i in range(N):
	(x, y, z) = map(int, input().split())
	if z in D:
		if y in D[z]:
			D[z][y].append((x, i))
		else:
			D[z][y] = [(x, i)]
	else:
		D[z] = {y: [(x, i)]}
E = {}
for z in D:
	for y in D[z]:
		D[z][y] = sorted(D[z][y])
		while len(D[z][y]) >= 2:
			(a, b) = (D[z][y].pop(), D[z][y].pop())
			ans.append((a[1], b[1]))
		if len(D[z][y]):
			if z in E:
				E[z].append((y, D[z][y][0][1]))
			else:
				E[z] = [(y, D[z][y][0][1])]
F = []
for z in E:
	E[z] = sorted(E[z])
	while len(E[z]) >= 2:
		(a, b) = (E[z].pop(), E[z].pop())
		ans.append((a[1], b[1]))
	if len(E[z]):
		F.append((z, E[z][0][1]))
F = sorted(F)
while len(F) >= 2:
	(a, b) = (F.pop(), F.pop())
	ans.append((a[1], b[1]))
ans = [(a[0] + 1, a[1] + 1) for a in ans]
sans = [' '.join(map(str, a)) for a in ans]
print('\n'.join(sans))


def d(le):
	for i in range(0, len(le), 2):
		print(le[i][3], le[i + 1][3])

def dd(it):
	global do
	tt = {}
	ddd = []
	it.sort(key=lambda x: x[1])
	l = list(set([i[1] for i in it]))
	l.sort()
	for i in l:
		tt[i] = []
	for i in it:
		tt[i[1]].append(i)
	for i in l:
		x = tt[i]
		if len(x) % 2 == 1:
			ddd.append(x[-1][:])
			x = x[:-1]
		if len(x) > 0:
			x.sort(key=lambda x: x[0])
			d(x[:])
	if len(ddd) % 2 == 1:
		do.append(ddd[-1][:])
		ddd = ddd[:-1]
	if len(ddd) > 0:
		ddd.sort(key=lambda x: x[1])
		d(ddd)
n = int(input())
it = []
for i in range(n):
	it.append(list(map(int, input().split())) + [i + 1])
ss = {}
it.sort(key=lambda x: [x[2], x[1], x[0], x[3]])
l = list(set([i[2] for i in it]))
l.sort()
for i in l:
	ss[i] = []
for i in it:
	ss[i[2]].append(i)
do = []
for i in l:
	x = ss[i]
	dd(x[:])
d(do)


import sys
import os
from io import IOBase, BytesIO

def solve(n, points):
	for i in range(n):
		points[i].append(i + 1)
	points.sort()
	points += [(float('inf'),) * 3]
	rem = []
	i = 0
	while i < n:
		if points[i][:2] == points[i + 1][:2]:
			print(points[i][3], points[i + 1][3])
			i += 2
		else:
			rem.append(i)
			i += 1
	rem.append(n)
	rem2 = []
	i = 0
	while i < len(rem) - 1:
		if points[rem[i]][0] == points[rem[i + 1]][0]:
			print(points[rem[i]][3], points[rem[i + 1]][3])
			i += 2
		else:
			rem2.append(points[rem[i]][3])
			i += 1
	for i in range(0, len(rem2), 2):
		print(rem2[i], rem2[i + 1])

def main():
	n = int(input())
	points = [[int(c) for c in input().split()] for _ in range(n)]
	solve(n, points)
BUFSIZE = 8192

class FastIO(BytesIO):
	newlines = 0

	def __init__(self, file):
		self._file = file
		self._fd = file.fileno()
		self.writable = 'x' in file.mode or 'w' in file.mode
		self.write = super(FastIO, self).write if self.writable else None

	def _fill(self):
		s = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
		self.seek((self.tell(), self.seek(0, 2), super(FastIO, self).write(s))[0])
		return s

	def read(self):
		while self._fill():
			pass
		return super(FastIO, self).read()

	def readline(self):
		while self.newlines == 0:
			s = self._fill()
			self.newlines = s.count(b'\n') + (not s)
		self.newlines -= 1
		return super(FastIO, self).readline()

	def flush(self):
		if self.writable:
			os.write(self._fd, self.getvalue())
			(self.truncate(0), self.seek(0))

class IOWrapper(IOBase):

	def __init__(self, file):
		self.buffer = FastIO(file)
		self.flush = self.buffer.flush
		self.writable = self.buffer.writable
		self.write = lambda s: self.buffer.write(s.encode('ascii'))
		self.read = lambda : self.buffer.read().decode('ascii')
		self.readline = lambda : self.buffer.readline().decode('ascii')
(sys.stdin, sys.stdout) = (IOWrapper(sys.stdin), IOWrapper(sys.stdout))

def input():
	return sys.stdin.readline().rstrip('\r\n')
main()


n = int(input())
a = [tuple(map(int, input().split())) for _ in range(n)]
s = {a[q]: q + 1 for q in range(n)}
a.sort()
(q, q1) = (0, 1)
(d, d1, d2) = ([[[a[0]]]], [], [])
while q1 < n:
	while q1 < n and a[q][0] == a[q1][0]:
		while q1 < n and a[q][1] == a[q1][1]:
			d[-1][-1].append(a[q1])
			q1 += 1
		if q1 < n and a[q][0] == a[q1][0]:
			d[-1].append([a[q1]])
			q = q1
			q1 += 1
	if q1 < n:
		d.append([[a[q1]]])
		q = q1
		q1 += 1
for q in range(len(d)):
	for q1 in range(len(d[q])):
		for q2 in range(1, len(d[q][q1]), 2):
			print(s[d[q][q1][q2 - 1]], s[d[q][q1][q2]])
		if len(d[q][q1]) % 2 == 1:
			d[q][q1] = d[q][q1][-1]
		else:
			d[q][q1] = -1
for q in range(len(d)):
	d1.append([])
	for q1 in range(len(d[q])):
		if d[q][q1] != -1:
			d1[-1].append(d[q][q1])
for q in range(len(d1)):
	for q1 in range(1, len(d1[q]), 2):
		print(s[d1[q][q1 - 1]], s[d1[q][q1]])
	if len(d1[q]) % 2 == 1:
		d2.append(d1[q][-1])
for q in range(1, len(d2), 2):
	print(s[d2[q - 1]], s[d2[q]])


from sys import stdin

def input():
	return stdin.readline()[:-1]

def intput():
	return int(input())

def sinput():
	return input().split()

def intsput():
	return tuple(map(int, sinput()))

def solve1d(points):
	points.sort()
	rem = False
	if len(points) % 2:
		rem = points.pop()
	return [points, rem]

def solve2d(points):
	solut = []
	rem = False
	groups = {}
	for p in points:
		if p[1] not in groups:
			groups[p[1]] = []
		groups[p[1]].append(p)
	gg = sorted(groups.values(), key=lambda x: x[0][1])
	for gridx in range(len(gg)):
		gr = gg[gridx]
		abc = solve1d(gr)
		solut += abc[0]
		if abc[1] and gridx < len(gg) - 1:
			testing = sorted(gg[gridx + 1], key=lambda x: abs(x[0] - abc[1][0]))
			tget = testing[0]
			solut.append(abc[1])
			solut.append(tget)
			gg[gridx + 1].remove(tget)
		elif abc[1]:
			rem = abc[1]
	return [solut, rem]

def solve3d(points):
	solut = []
	rem = False
	groups = {}
	for p in points:
		if p[2] not in groups:
			groups[p[2]] = []
		groups[p[2]].append(p)
	gg = sorted(groups.values(), key=lambda x: x[0][2])
	for gridx in range(len(gg)):
		gr = gg[gridx]
		abc = solve2d(gr)
		solut += abc[0]
		if abc[1] and gridx < len(gg) - 1:
			testing = sorted(gg[gridx + 1], key=lambda x: (abs(x[0] - abc[1][0]), abs(x[1] - abc[1][1])))
			tget = testing[0]
			solut.append(abc[1])
			solut.append(tget)
			gg[gridx + 1].remove(tget)
		elif abc[1]:
			rem = abc[1]
	return [solut, rem]
n = intput()
cod = [intsput() for _ in range(n)]
(pp, r) = solve3d(cod)
idxtable = {}
for i in range(n):
	idxtable[cod[i]] = i
for i in range(len(pp) // 2):
	print(idxtable[pp[i * 2]] + 1, idxtable[pp[i * 2 + 1]] + 1)


import os, sys
from io import BytesIO, IOBase
from collections import defaultdict
left = []

def fun(lst, co):
	global left
	dctx = defaultdict(list)
	leftx = []
	for i in lst:
		dctx[co[i][0]].append(i)
	for i in dctx.values():
		for j in range(len(i) // 2):
			print(i[2 * j] + 1, i[2 * j + 1] + 1)
		if len(i) & 1:
			leftx.append(i[-1])
	leftx.sort(key=lambda xx: co[xx][0])
	for i in range(len(leftx) // 2):
		print(leftx[2 * i] + 1, leftx[2 * i + 1] + 1)
	if len(leftx) & 1:
		left.append(leftx[-1])

def main():
	global left
	n = int(input())
	co = [list(map(int, input().split())) for _ in range(n)]
	orde = sorted(range(n), key=lambda xx: co[xx][1])
	dctz = defaultdict(list)
	for i in orde:
		dctz[co[i][2]].append(i)
	for i in dctz.values():
		fun(i, co)
	left.sort(key=lambda xx: co[xx][2])
	for i in range(len(left) // 2):
		print(left[2 * i] + 1, left[2 * i + 1] + 1)
BUFSIZE = 8192

class FastIO(IOBase):
	newlines = 0

	def __init__(self, file):
		self._fd = file.fileno()
		self.buffer = BytesIO()
		self.writable = 'x' in file.mode or 'r' not in file.mode
		self.write = self.buffer.write if self.writable else None

	def read(self):
		while True:
			b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
			if not b:
				break
			ptr = self.buffer.tell()
			(self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr))
		self.newlines = 0
		return self.buffer.read()

	def readline(self):
		while self.newlines == 0:
			b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
			self.newlines = b.count(b'\n') + (not b)
			ptr = self.buffer.tell()
			(self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr))
		self.newlines -= 1
		return self.buffer.readline()

	def flush(self):
		if self.writable:
			os.write(self._fd, self.buffer.getvalue())
			(self.buffer.truncate(0), self.buffer.seek(0))

class IOWrapper(IOBase):

	def __init__(self, file):
		self.buffer = FastIO(file)
		self.flush = self.buffer.flush
		self.writable = self.buffer.writable
		self.write = lambda s: self.buffer.write(s.encode('ascii'))
		self.read = lambda : self.buffer.read().decode('ascii')
		self.readline = lambda : self.buffer.readline().decode('ascii')
(sys.stdin, sys.stdout) = (IOWrapper(sys.stdin), IOWrapper(sys.stdout))
input = lambda : sys.stdin.readline().rstrip('\r\n')
main()


import sys
import math
input = sys.stdin.readline
n = int(input())
arr = []
for i in range(n):
	arr.append(list(map(int, input().split())))
	arr[-1].append(i + 1)
ans = []
arr.sort()
done = [0] * n
i = 0
j = 1
while i < n and j < n:
	if arr[i][0] == arr[j][0] and arr[i][1] == arr[j][1]:
		ans.append([arr[i][3], arr[j][3]])
		done[arr[i][3] - 1] += 1
		done[arr[j][3] - 1] += 1
		i += 2
		j += 2
	else:
		i += 1
		j += 1
arr1 = []
for i in range(n):
	if done[arr[i][3] - 1] == 0:
		arr1.append(arr[i])
n = len(arr1)
i = 0
j = 1
while i < n and j < n:
	if arr1[i][0] == arr1[j][0]:
		ans.append([arr1[i][3], arr1[j][3]])
		done[arr1[i][3] - 1] += 1
		done[arr1[j][3] - 1] += 1
		i += 2
		j += 2
	else:
		i += 1
		j += 1
arr2 = []
for i in range(n):
	if done[arr1[i][3] - 1] == 0:
		arr2.append(arr1[i])
n = len(arr2)
for i in range(n):
	if i % 2 == 0:
		ans.append([arr2[i][3], arr2[i + 1][3]])
for i in range(len(ans)):
	print(*ans[i])


def main():
	n = int(input())
	lkz = {}
	lky = {}
	for i in range(n):
		(px, py, pz) = map(int, input().split())
		if pz not in lkz:
			lkz[pz] = set()
			lkz[pz].add(py)
			lky[pz, py] = [(pz, py, px, i + 1)]
		else:
			lkz[pz].add(py)
			if (pz, py) not in lky:
				lky[pz, py] = [(pz, py, px, i + 1)]
			else:
				lky[pz, py].append((pz, py, px, i + 1))
	ans = []
	final_list = []
	for pz in lkz:
		curr_list = []
		for py in lkz[pz]:
			if len(lky[pz, py]) > 1:
				lky[pz, py].sort()
				for i in range(0, len(lky[pz, py]) // 2):
					p1 = lky[pz, py][2 * i]
					p2 = lky[pz, py][2 * i + 1]
					ans.append((p1[3], p2[3]))
			if len(lky[pz, py]) % 2 == 1:
				curr_list.append(lky[pz, py][-1])
		if len(curr_list) > 1:
			curr_list.sort()
			for i in range(0, len(curr_list) // 2):
				ans.append((curr_list[2 * i][3], curr_list[2 * i + 1][3]))
		if len(curr_list) % 2 == 1:
			final_list.append(curr_list[-1])
	final_list.sort()
	for i in range(0, len(final_list) // 2):
		ans.append((final_list[2 * i][3], final_list[2 * i + 1][3]))
	for pair in ans:
		print(*pair)
main()


from bisect import bisect

def solve(points):

	def it():
		Z = sorted(set((z for (x, y, z) in points)))
		z_bin = [[] for _ in range(len(Z))]
		for (i, (x, y, z)) in enumerate(points):
			z_bin[bisect(Z, z) - 1].append(i)
		last_z = -1
		for (zi, plane) in enumerate(z_bin):
			Y = sorted(set((points[i][1] for i in plane)))
			y_bin = [[] for _ in range(len(Y))]
			for i in plane:
				(x, y, z) = points[i]
				y_bin[bisect(Y, y) - 1].append(i)
			last_y = -1
			for (yi, line) in enumerate(y_bin):
				line.sort(key=lambda i: points[i][0])
				m = iter(line)
				for (a, b) in zip(m, m):
					yield (a, b)
				if len(line) % 2:
					if last_y < 0:
						last_y = line[-1]
					else:
						yield (last_y, line[-1])
						last_y = -1
			if last_y >= 0:
				if last_z < 0:
					last_z = last_y
				else:
					yield (last_z, last_y)
					last_z = -1
	return it()
import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
N = int(readline())
m = map(int, read().split())
res = solve(tuple(zip(m, m, m)))
print('\n'.join((f'{a + 1} {b + 1}' for (a, b) in res)))


import os
import sys
import math
from io import BytesIO, IOBase
import io
from fractions import Fraction
import collections
from itertools import permutations
from collections import defaultdict
from collections import deque
from collections import Counter
import threading
BUFSIZE = 8192

class FastIO(IOBase):
	newlines = 0

	def __init__(self, file):
		self._fd = file.fileno()
		self.buffer = BytesIO()
		self.writable = 'x' in file.mode or 'r' not in file.mode
		self.write = self.buffer.write if self.writable else None

	def read(self):
		while True:
			b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
			if not b:
				break
			ptr = self.buffer.tell()
			(self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr))
		self.newlines = 0
		return self.buffer.read()

	def readline(self):
		while self.newlines == 0:
			b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
			self.newlines = b.count(b'\n') + (not b)
			ptr = self.buffer.tell()
			(self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr))
		self.newlines -= 1
		return self.buffer.readline()

	def flush(self):
		if self.writable:
			os.write(self._fd, self.buffer.getvalue())
			(self.buffer.truncate(0), self.buffer.seek(0))

class IOWrapper(IOBase):

	def __init__(self, file):
		self.buffer = FastIO(file)
		self.flush = self.buffer.flush
		self.writable = self.buffer.writable
		self.write = lambda s: self.buffer.write(s.encode('ascii'))
		self.read = lambda : self.buffer.read().decode('ascii')
		self.readline = lambda : self.buffer.readline().decode('ascii')
(sys.stdin, sys.stdout) = (IOWrapper(sys.stdin), IOWrapper(sys.stdout))
input = lambda : sys.stdin.readline().rstrip('\r\n')

class SegmentTree:

	def __init__(self, data, default=0, func=lambda a, b: max(a, b)):
		self._default = default
		self._func = func
		self._len = len(data)
		self._size = _size = 1 << (self._len - 1).bit_length()
		self.data = [default] * (2 * _size)
		self.data[_size:_size + self._len] = data
		for i in reversed(range(_size)):
			self.data[i] = func(self.data[i + i], self.data[i + i + 1])

	def __delitem__(self, idx):
		self[idx] = self._default

	def __getitem__(self, idx):
		return self.data[idx + self._size]

	def __setitem__(self, idx, value):
		idx += self._size
		self.data[idx] = value
		idx >>= 1
		while idx:
			self.data[idx] = self._func(self.data[2 * idx], self.data[2 * idx + 1])
			idx >>= 1

	def __len__(self):
		return self._len

	def query(self, start, stop):
		if start == stop:
			return self.__getitem__(start)
		stop += 1
		start += self._size
		stop += self._size
		res = self._default
		while start < stop:
			if start & 1:
				res = self._func(res, self.data[start])
				start += 1
			if stop & 1:
				stop -= 1
				res = self._func(res, self.data[stop])
			start >>= 1
			stop >>= 1
		return res

	def __repr__(self):
		return 'SegmentTree({0})'.format(self.data)

class SegmentTree1:

	def __init__(self, data, default=0, func=lambda a, b: a + b):
		self._default = default
		self._func = func
		self._len = len(data)
		self._size = _size = 1 << (self._len - 1).bit_length()
		self.data = [default] * (2 * _size)
		self.data[_size:_size + self._len] = data
		for i in reversed(range(_size)):
			self.data[i] = func(self.data[i + i], self.data[i + i + 1])

	def __delitem__(self, idx):
		self[idx] = self._default

	def __getitem__(self, idx):
		return self.data[idx + self._size]

	def __setitem__(self, idx, value):
		idx += self._size
		self.data[idx] = value
		idx >>= 1
		while idx:
			self.data[idx] = self._func(self.data[2 * idx], self.data[2 * idx + 1])
			idx >>= 1

	def __len__(self):
		return self._len

	def query(self, start, stop):
		if start == stop:
			return self.__getitem__(start)
		stop += 1
		start += self._size
		stop += self._size
		res = self._default
		while start < stop:
			if start & 1:
				res = self._func(res, self.data[start])
				start += 1
			if stop & 1:
				stop -= 1
				res = self._func(res, self.data[stop])
			start >>= 1
			stop >>= 1
		return res

	def __repr__(self):
		return 'SegmentTree({0})'.format(self.data)
MOD = 10 ** 9 + 7

class Factorial:

	def __init__(self, MOD):
		self.MOD = MOD
		self.factorials = [1, 1]
		self.invModulos = [0, 1]
		self.invFactorial_ = [1, 1]

	def calc(self, n):
		if n <= -1:
			print('Invalid argument to calculate n!')
			print('n must be non-negative value. But the argument was ' + str(n))
			exit()
		if n < len(self.factorials):
			return self.factorials[n]
		nextArr = [0] * (n + 1 - len(self.factorials))
		initialI = len(self.factorials)
		prev = self.factorials[-1]
		m = self.MOD
		for i in range(initialI, n + 1):
			prev = nextArr[i - initialI] = prev * i % m
		self.factorials += nextArr
		return self.factorials[n]

	def inv(self, n):
		if n <= -1:
			print('Invalid argument to calculate n^(-1)')
			print('n must be non-negative value. But the argument was ' + str(n))
			exit()
		p = self.MOD
		pi = n % p
		if pi < len(self.invModulos):
			return self.invModulos[pi]
		nextArr = [0] * (n + 1 - len(self.invModulos))
		initialI = len(self.invModulos)
		for i in range(initialI, min(p, n + 1)):
			next = -self.invModulos[p % i] * (p // i) % p
			self.invModulos.append(next)
		return self.invModulos[pi]

	def invFactorial(self, n):
		if n <= -1:
			print('Invalid argument to calculate (n^(-1))!')
			print('n must be non-negative value. But the argument was ' + str(n))
			exit()
		if n < len(self.invFactorial_):
			return self.invFactorial_[n]
		self.inv(n)
		nextArr = [0] * (n + 1 - len(self.invFactorial_))
		initialI = len(self.invFactorial_)
		prev = self.invFactorial_[-1]
		p = self.MOD
		for i in range(initialI, n + 1):
			prev = nextArr[i - initialI] = prev * self.invModulos[i % p] % p
		self.invFactorial_ += nextArr
		return self.invFactorial_[n]

class Combination:

	def __init__(self, MOD):
		self.MOD = MOD
		self.factorial = Factorial(MOD)

	def ncr(self, n, k):
		if k < 0 or n < k:
			return 0
		k = min(k, n - k)
		f = self.factorial
		return f.calc(n) * f.invFactorial(max(n - k, k)) * f.invFactorial(min(k, n - k)) % self.MOD
mod = 10 ** 9 + 7
omod = 998244353
prime = [True for i in range(10001)]
prime[0] = prime[1] = False

def SieveOfEratosthenes(n=10000):
	p = 2
	c = 0
	while p <= n:
		if prime[p] == True:
			c += 1
			for i in range(p, n + 1, p):
				prime[i] = False
		p += 1

class DSU:

	def __init__(self, R, C):
		self.par = range(R * C + 1)
		self.rnk = [0] * (R * C + 1)
		self.sz = [1] * (R * C + 1)

	def find(self, x):
		if self.par[x] != x:
			self.par[x] = self.find(self.par[x])
		return self.par[x]

	def union(self, x, y):
		(xr, yr) = (self.find(x), self.find(y))
		if xr == yr:
			return
		if self.rnk[xr] < self.rnk[yr]:
			(xr, yr) = (yr, xr)
		if self.rnk[xr] == self.rnk[yr]:
			self.rnk[xr] += 1
		self.par[yr] = xr
		self.sz[xr] += self.sz[yr]

	def size(self, x):
		return self.sz[self.find(x)]

	def top(self):
		return self.size(len(self.sz) - 1) - 1

class LazySegTree:

	def __init__(self, _op, _e, _mapping, _composition, _id, v):

		def set(p, x):
			assert 0 <= p < _n
			p += _size
			for i in range(_log, 0, -1):
				_push(p >> i)
			_d[p] = x
			for i in range(1, _log + 1):
				_update(p >> i)

		def get(p):
			assert 0 <= p < _n
			p += _size
			for i in range(_log, 0, -1):
				_push(p >> i)
			return _d[p]

		def prod(l, r):
			assert 0 <= l <= r <= _n
			if l == r:
				return _e
			l += _size
			r += _size
			for i in range(_log, 0, -1):
				if l >> i << i != l:
					_push(l >> i)
				if r >> i << i != r:
					_push(r >> i)
			sml = _e
			smr = _e
			while l < r:
				if l & 1:
					sml = _op(sml, _d[l])
					l += 1
				if r & 1:
					r -= 1
					smr = _op(_d[r], smr)
				l >>= 1
				r >>= 1
			return _op(sml, smr)

		def apply(l, r, f):
			assert 0 <= l <= r <= _n
			if l == r:
				return
			l += _size
			r += _size
			for i in range(_log, 0, -1):
				if l >> i << i != l:
					_push(l >> i)
				if r >> i << i != r:
					_push(r - 1 >> i)
			l2 = l
			r2 = r
			while l < r:
				if l & 1:
					_all_apply(l, f)
					l += 1
				if r & 1:
					r -= 1
					_all_apply(r, f)
				l >>= 1
				r >>= 1
			l = l2
			r = r2
			for i in range(1, _log + 1):
				if l >> i << i != l:
					_update(l >> i)
				if r >> i << i != r:
					_update(r - 1 >> i)

		def _update(k):
			_d[k] = _op(_d[2 * k], _d[2 * k + 1])

		def _all_apply(k, f):
			_d[k] = _mapping(f, _d[k])
			if k < _size:
				_lz[k] = _composition(f, _lz[k])

		def _push(k):
			_all_apply(2 * k, _lz[k])
			_all_apply(2 * k + 1, _lz[k])
			_lz[k] = _id
		_n = len(v)
		_log = _n.bit_length()
		_size = 1 << _log
		_d = [_e] * (2 * _size)
		_lz = [_id] * _size
		for i in range(_n):
			_d[_size + i] = v[i]
		for i in range(_size - 1, 0, -1):
			_update(i)
		self.set = set
		self.get = get
		self.prod = prod
		self.apply = apply
MIL = 1 << 20

def makeNode(total, count):
	return total * MIL + count

def getTotal(node):
	return math.floor(node / MIL)

def getCount(node):
	return node - getTotal(node) * MIL
nodeIdentity = makeNode(0.0, 0.0)

def nodeOp(node1, node2):
	return node1 + node2
	return makeNode(getTotal(node1) + getTotal(node2), getCount(node1) + getCount(node2))
identityMapping = -1

def mapping(tag, node):
	if tag == identityMapping:
		return node
	count = getCount(node)
	return makeNode(tag * count, count)

def composition(mapping1, mapping2):
	return mapping1 if mapping1 != identityMapping else mapping2

def memodict(f):

	class memodict(dict):

		def __missing__(self, key):
			ret = self[key] = f(key)
			return ret
	return memodict().__getitem__

def pollard_rho(n):
	if n & 1 == 0:
		return 2
	if n % 3 == 0:
		return 3
	s = (n - 1 & 1 - n).bit_length() - 1
	d = n >> s
	for a in [2, 325, 9375, 28178, 450775, 9780504, 1795265022]:
		p = pow(a, d, n)
		if p == 1 or p == n - 1 or a % n == 0:
			continue
		for _ in range(s):
			prev = p
			p = p * p % n
			if p == 1:
				return math.gcd(prev - 1, n)
			if p == n - 1:
				break
		else:
			for i in range(2, n):
				(x, y) = (i, (i * i + 1) % n)
				f = math.gcd(abs(x - y), n)
				while f == 1:
					(x, y) = ((x * x + 1) % n, (y * y + 1) % n)
					y = (y * y + 1) % n
					f = math.gcd(abs(x - y), n)
				if f != n:
					return f
	return n

@memodict
def prime_factors(n):
	if n <= 1:
		return Counter()
	f = pollard_rho(n)
	return Counter([n]) if f == n else prime_factors(f) + prime_factors(n // f)

def distinct_factors(n):
	factors = [1]
	for (p, exp) in prime_factors(n).items():
		factors += [p ** i * factor for factor in factors for i in range(1, exp + 1)]
	return factors

def all_factors(n):
	(small, large) = ([], [])
	for i in range(1, int(n ** 0.5) + 1, 2 if n & 1 else 1):
		if not n % i:
			small.append(i)
			large.append(n // i)
	if small[-1] == large[-1]:
		large.pop()
	large.reverse()
	small.extend(large)
	return small

def binarySearch(arr, n, i, key):
	left = 0
	right = n - 1
	mid = 0
	res = n
	while left <= right:
		mid = (right + left) // 2
		if arr[mid][i] > key:
			res = mid
			right = mid - 1
		else:
			left = mid + 1
	return res

def binarySearch1(arr, n, i, key):
	left = 0
	right = n - 1
	mid = 0
	res = -1
	while left <= right:
		mid = (right + left) // 2
		if arr[mid][i] > key:
			right = mid - 1
		else:
			res = mid
			left = mid + 1
	return res
n = int(input())
arr = []
for i in range(n):
	(a, b, c) = map(int, input().split())
	arr.append([a, b, c] + [i + 1])
arr.sort()
ans = []
for i in range(2, -1, -1):
	st = []
	for x in arr:
		if st and all((st[-1][itr] <= x[itr] for itr in range(i + 1))):
			ans.append((st.pop()[-1], x[-1]))
		else:
			st.append(x)
	arr = st
for i in ans:
	print(i[0], i[1])


import io, os
input = io.BytesIO(os.read(0, os.fstat(0).st_size)).readline
import math
n = int(input())
points = []
seq = []
for i in range(n):
	(x, y, z) = map(int, input().split())
	points.append([x, y, z, i])
points = sorted(points, key=lambda x: [x[2], x[1], x[0], x[3]])

def focusy(y, temp):
	newtemp = []
	rest = []
	cout = 0
	while temp and temp[-1][1] == y:
		newtemp.append(temp.pop())
	if len(newtemp) % 2 == 1:
		rest = newtemp[-1]
	num = len(newtemp) // 2
	for i in range(num):
		seq.append(newtemp[2 * i][3])
		seq.append(newtemp[2 * i + 1][3])
	return rest

def focusz(z, temp):
	newtemp = []
	while temp and temp[-1][2] == z:
		newtemp.append(points.pop())
	rest = []
	finalrest = []
	while newtemp:
		temprest = focusy(newtemp[-1][1], newtemp)
		if temprest:
			rest.append(temprest)
	if len(rest) % 2 == 1:
		finalrest = rest[-1]
	num = len(rest) // 2
	for i in range(num):
		seq.append(rest[2 * i][3])
		seq.append(rest[2 * i + 1][3])
	return finalrest
finalrest = []
while points:
	tempfinal = focusz(points[-1][2], points)
	if tempfinal:
		finalrest.append(tempfinal)
num = len(finalrest) // 2
for i in range(num):
	seq.append(finalrest[2 * i][3])
	seq.append(finalrest[2 * i + 1][3])
for i in range(len(seq) // 2):
	print(seq[2 * i] + 1, seq[2 * i + 1] + 1)


from sys import stdin, setrecursionlimit
setrecursionlimit(10 ** 7)

def iin():
	return int(stdin.readline())

def lin():
	return list(map(int, stdin.readline().split()))

def main():
	n = iin()
	point = [lin() + [i + 1] for i in range(n)]
	point.sort(reverse=True)
	p1 = []
	while point:
		(x, y, z, pos) = point.pop()
		if len(point) > 0 and x == point[-1][0] and (y == point[-1][1]):
			(x1, y1, z1, pos1) = point.pop()
			print(pos, pos1)
		else:
			p1.append([x, y, z, pos])
	point = p1
	point.sort(reverse=True)
	p1 = []
	while point:
		(x, y, z, pos) = point.pop()
		if len(point) > 0 and x == point[-1][0]:
			p2 = point.pop()
			print(pos, p2[3])
		else:
			p1.append([x, y, z, pos])
	point = p1
	point.sort(reverse=True)
	for i in range(0, len(point), 2):
		print(point[i][3], point[i + 1][3])
main()


from collections import defaultdict

def filterOut(ans, removed, mapp):
	for v in mapp.values():
		arr = list(v)
		n = len(arr)
		arr.sort()
		i = 0
		while i + 1 < n:
			(idx1, idx2) = (arr[i][1], arr[i + 1][1])
			ans.append([idx1, idx2])
			removed[idx1] = removed[idx2] = True
			i += 2
	return

def filterOut2(ans, removed, mapp):
	for v in mapp.values():
		arr = list(v)
		n = len(arr)
		arr.sort()
		i = 0
		while i + 1 < n:
			(idx1, idx2) = (arr[i][2], arr[i + 1][2])
			ans.append([idx1, idx2])
			removed[idx1] = removed[idx2] = True
			i += 2
	return

def main():
	n = int(input())
	coords = []
	for i in range(1, n + 1):
		(x, y, z) = readIntArr()
		coords.append([x, y, z, i])
	ans = []
	removed = [False for _ in range(n + 1)]
	xyMap = defaultdict(lambda : [])
	for i in range(n):
		(x, y, z, idx) = coords[i]
		xyMap[x, y].append([z, idx])
	filterOut(ans, removed, xyMap)
	coords2 = []
	for i in range(n):
		if not removed[coords[i][3]]:
			coords2.append(coords[i])
	coords = coords2
	n = len(coords)
	yzMap = defaultdict(lambda : [])
	for i in range(n):
		(x, y, z, idx) = coords[i]
		yzMap[y, z].append([x, idx])
	filterOut(ans, removed, yzMap)
	coords2 = []
	for i in range(n):
		if not removed[coords[i][3]]:
			coords2.append(coords[i])
	coords = coords2
	n = len(coords)
	zxMap = defaultdict(lambda : [])
	for i in range(n):
		(x, y, z, idx) = coords[i]
		zxMap[z, x].append([y, idx])
	filterOut(ans, removed, zxMap)
	coords2 = []
	for i in range(n):
		if not removed[coords[i][3]]:
			coords2.append(coords[i])
	coords = coords2
	n = len(coords)
	xMap = defaultdict(lambda : [])
	for i in range(n):
		(x, y, z, idx) = coords[i]
		xMap[x].append([y, z, idx])
	filterOut2(ans, removed, xMap)
	coords2 = []
	for i in range(n):
		if not removed[coords[i][3]]:
			coords2.append(coords[i])
	coords = coords2
	n = len(coords)
	yMap = defaultdict(lambda : [])
	for i in range(n):
		(x, y, z, idx) = coords[i]
		yMap[y].append([x, z, idx])
	filterOut2(ans, removed, yMap)
	coords2 = []
	for i in range(n):
		if not removed[coords[i][3]]:
			coords2.append(coords[i])
	coords = coords2
	n = len(coords)
	zMap = defaultdict(lambda : [])
	for i in range(n):
		(x, y, z, idx) = coords[i]
		zMap[x].append([y, z, idx])
	filterOut2(ans, removed, zMap)
	coords2 = []
	for i in range(n):
		if not removed[coords[i][3]]:
			coords2.append(coords[i])
	coords = coords2
	n = len(coords)
	coords.sort()
	for i in range(0, n, 2):
		ans.append([coords[i][3], coords[i + 1][3]])
	multiLineArrayOfArraysPrint(ans)
	return
import sys
input = lambda : sys.stdin.readline().rstrip('\r\n')

def oneLineArrayPrint(arr):
	print(' '.join([str(x) for x in arr]))

def multiLineArrayPrint(arr):
	print('\n'.join([str(x) for x in arr]))

def multiLineArrayOfArraysPrint(arr):
	print('\n'.join([' '.join([str(x) for x in y]) for y in arr]))

def readIntArr():
	return [int(x) for x in input().split()]

def makeArr(defaultValFactory, dimensionArr):
	dv = defaultValFactory
	da = dimensionArr
	if len(da) == 1:
		return [dv() for _ in range(da[0])]
	else:
		return [makeArr(dv, da[1:]) for _ in range(da[0])]

def queryInteractive(i, j):
	print('? {} {}'.format(i, j))
	sys.stdout.flush()
	return int(input())

def answerInteractive(ans):
	print('! {}'.format(' '.join([str(x) for x in ans])))
	sys.stdout.flush()
inf = float('inf')
MOD = 10 ** 9 + 7
for _abc in range(1):
	main()


from sys import stdin
input = stdin.readline
n = int(input())
l = [list(map(int, input().split())) for i in range(n)]
a = [[l[i], i + 1] for i in range(n)]
used = [0] * (n + 1)
a.sort()
d = {}
for i in a:
	d[i[0][0]] = []
for i in a:
	d[i[0][0]].append([i[0][1], i[0][2], i[1]])
for x in d:
	l = d[x]
	b = {}
	for i in l:
		b[i[0]] = []
	for i in l:
		b[i[0]].append([i[1], i[2]])
	for y in b:
		pom = 0
		while pom + 1 < len(b[y]):
			print(b[y][pom][1], b[y][pom + 1][1])
			used[b[y][pom][1]] = 1
			used[b[y][pom + 1][1]] = 1
			pom += 2
	c = []
	for gg in l:
		if used[gg[2]] == 0:
			c.append(gg)
	cc = [[c[gg][0], c[gg][2]] for gg in range(len(c))]
	g = 0
	while g < len(cc) - 1:
		print(cc[g][-1], cc[g + 1][-1])
		used[cc[g][-1]] = 1
		used[cc[g + 1][-1]] = 1
		g += 2
c = []
for i in range(0, n):
	if used[a[i][1]] == 0:
		c.append([a[i][0][0], a[i][1]])
c.sort()
i = 0
while i < len(c) - 1:
	print(c[i][1], c[i + 1][1])
	i += 2


def solve(points, ans, coords, x):
	arr = []
	curr = []
	y = points[0][0]
	for p in points:
		if p[0] == y:
			curr.append((y, p[1], p[2]))
		else:
			arr.append(curr)
			y = p[0]
			curr = [(y, p[1], p[2])]
	arr.append(curr)
	arr1 = []
	for i in arr:
		while len(i) >= 2:
			ans.append((i.pop(0)[2], i.pop(0)[2]))
		if len(i) == 1:
			arr1.append((i[0][0], i[0][1], i[0][2]))
	while len(arr1) >= 2:
		ans.append((arr1.pop(0)[2], arr1.pop(0)[2]))
	coords[x] = arr1[:]

def main():
	n = int(input())
	points = []
	coords = {}
	for i in range(n):
		(x, y, z) = list(map(int, input().split()))
		if x not in list(coords.keys()):
			coords[x] = [(y, z, i + 1)]
		else:
			coords[x].append((y, z, i + 1))
	ans = []
	for i in list(coords.keys()):
		coords[i].sort()
		if len(coords[i]) > 1:
			solve(coords[i], ans, coords, i)
		if len(coords[i]) == 1:
			points.append((i, coords[i][0][0], coords[i][0][1], coords[i][0][2]))
	points.sort()
	for i in range(0, len(points), 2):
		(a, b) = (points[i][3], points[i + 1][3])
		ans.append((a, b))
	for i in ans:
		print(i[0], i[1])
main()


n = int(input())
li = []
for i in range(n):
	(a, b, c) = map(int, input().split())
	li.append([a, b, c, i + 1])
li.sort()
i = 0
l = len(li)
a = []
while i < l:
	if i < l - 1 and li[i][:2] == li[i + 1][:2]:
		print(li[i][3], li[i + 1][3])
		i += 2
	else:
		a.append(li[i])
		i += 1
li = list(a)
l = len(li)
i = 0
a = []
while i < l:
	if i < l - 1 and li[i][0] == li[i + 1][0]:
		print(li[i][3], li[i + 1][3])
		i += 2
	else:
		a.append(li[i])
		i += 1
li = list(a)
l = len(li)
i = 0
while i < l - 1:
	print(li[i][3], li[i + 1][3])
	i += 2


from sys import stdin, stdout
n = int(stdin.readline())
l = []
for i in range(n):
	x = list(map(int, stdin.readline().split()))
	l.append([x, i + 1])
l.sort()
deleted = [0] * n
for i in range(n - 1):
	if deleted[i]:
		continue
	if l[i][0][0] == l[i + 1][0][0] and l[i][0][1] == l[i + 1][0][1]:
		print(l[i][1], l[i + 1][1])
		deleted[i] = deleted[i + 1] = 1
remaining = []
for i in range(n):
	if deleted[i] == 0:
		remaining.append(l[i])
del deleted
n = len(remaining)
deleted = [0] * n
for i in range(n - 1):
	if deleted[i]:
		continue
	if remaining[i][0][0] == remaining[i + 1][0][0]:
		print(remaining[i][1], remaining[i + 1][1])
		deleted[i] = deleted[i + 1] = 1
last = []
for i in range(n):
	if deleted[i] == 0:
		last.append(remaining[i])
for i in range(0, len(last), 2):
	print(last[i][1], last[i + 1][1])


import sys
from collections import defaultdict
readline = sys.stdin.readline
N = int(readline())
XYZ = [tuple(map(int, readline().split())) for _ in range(N)]
XYZI = [(x, y, z, i) for (i, (x, y, z)) in enumerate(XYZ, 1)]
XYZI.sort()
(X, Y, Z, IDX) = map(list, zip(*XYZI))
Di = defaultdict(list)
for i in range(N):
	(x, y, z, idx) = (X[i], Y[i], Z[i], IDX[i])
	Di[x].append((y, z, idx))
Ans = []
Ama = []
for L in Di.values():
	D2 = defaultdict(int)
	for (y, _, _) in L:
		D2[y] += 1
	pre = None
	st = None
	for (y, z, i) in L:
		if st is None and D2[y] == 1:
			if pre is not None:
				Ans.append((pre, i))
				pre = None
			else:
				pre = i
		elif st is not None:
			Ans.append((st, i))
			st = None
		else:
			st = i
		D2[y] -= 1
	if st:
		Ama.append(st)
	if pre:
		Ama.append(pre)
Le = len(Ama)
for i in range(Le // 2):
	Ans.append((Ama[2 * i], Ama[2 * i + 1]))
for a in Ans:
	sys.stdout.write('{} {}\n'.format(*a))


def solve_z(points):
	cur = None
	d = {}
	for p in points:
		if p[0] not in d:
			d[p[0]] = []
		d[p[0]].append(p)
	for k in d:
		d[k] = sorted(d[k], key=lambda x: x[1])
	for k in sorted(d.keys()):
		n = len(d[k])
		for i in range(0, n, 2):
			if i + 1 == n:
				if cur is None:
					cur = str(d[k][i][3])
				else:
					print(cur + ' ' + str(d[k][i][3]))
					cur = None
			else:
				(p1, p2) = (d[k][i][3], d[k][i + 1][3])
				print(str(p1) + ' ' + str(p2))
	return cur
n = int(input())
P = [list(map(int, input().split())) + [i + 1] for i in range(n)]
d_z = {}
for p in P:
	if p[2] not in d_z:
		d_z[p[2]] = []
	d_z[p[2]].append(p)
cur = None
for k in sorted(d_z.keys()):
	next_ = solve_z(d_z[k])
	if next_ is not None:
		if cur is None:
			cur = next_
		else:
			print(cur + ' ' + next_)
			cur = None


n = int(input())
arr = []
for _ in range(n):
	arr.append(list(map(int, input().split())) + [_ + 1])
arr.sort(key=lambda x: (x[0], x[1], x[2]))
res = []

def valid(pt1, pt2, axis):
	flag = 1
	for k in range(axis + 1):
		if pt1[k] > pt2[k]:
			flag = 0
			break
	return flag
for axis in range(2, -1, -1):
	stc = []
	for pt in arr:
		if stc and valid(stc[-1], pt, axis):
			res.append([stc.pop()[3], pt[3]])
		else:
			stc.append(pt)
	arr = stc
for pr in res:
	print(pr[0], pr[1])


import sys
input = sys.stdin.readline

def solve1d(a):
	a.sort()
	for i in range(0, len(a) - 1, 2):
		print(a[i][-1] + 1, a[i + 1][-1] + 1)
	if len(a) % 2:
		return a[-1]
	return False

def solve2d(start, end):
	d = {}
	for i in range(start, end + 1):
		if coor[i][1] not in d:
			d[coor[i][1]] = [[coor[i][0], coor[i][2], coor[i][3]]]
		else:
			d[coor[i][1]].append([coor[i][0], coor[i][2], coor[i][3]])
	left = []
	for i in d:
		x = solve1d(d[i])
		if x:
			left.append([i, x[1], x[-1]])
	left.sort()
	for i in range(0, len(left) - 1, 2):
		print(left[i][-1] + 1, left[i + 1][-1] + 1)
	if len(left) % 2:
		return left[-1]
	return False

def solve3d():
	coor.sort(key=lambda x: x[2])
	prev = 0
	left = []
	for i in range(1, n):
		if coor[i][2] != coor[prev][2]:
			x = solve2d(prev, i - 1)
			if x:
				left.append([x[1], x[-1]])
			prev = i
	x = solve2d(prev, n - 1)
	if x:
		left.append([x[1], x[-1]])
	left.sort()
	for i in range(0, len(left), 2):
		print(left[i][-1] + 1, left[i + 1][-1] + 1)
n = int(input())
coor = []
for i in range(n):
	coor.append(list(map(int, input().split())))
	coor[-1].append(i)
solve3d()


from __future__ import division, print_function
import bisect
import math
import heapq
import itertools
import sys
from collections import deque
from atexit import register
from collections import Counter
from functools import reduce
sys.setrecursionlimit(10000000)
if sys.version_info[0] < 3:
	from io import BytesIO as stream
else:
	from io import StringIO as stream
if sys.version_info[0] < 3:

	class dict(dict):

		def items(self):
			return dict.iteritems(self)

		def keys(self):
			return dict.iterkeys(self)

		def values(self):
			return dict.itervalues(self)
	input = raw_input
	range = xrange
	filter = itertools.ifilter
	map = itertools.imap
	zip = itertools.izip

def sync_with_stdio(sync=True):
	global input, flush
	if sync:
		flush = sys.stdout.flush
	else:
		sys.stdin = stream(sys.stdin.read())
		input = lambda : sys.stdin.readline().rstrip('\r\n')
		sys.stdout = stream()
		register(lambda : sys.__stdout__.write(sys.stdout.getvalue()))

def main():
	n = int(input())
	lol = []
	d = dict()
	d1 = dict()
	for i in range(n):
		(x, y, z) = map(int, input().split())
		lol.append([x, y, z, i + 1])
	lol.sort()
	for ii in range(n):
		x = lol[ii][0]
		y = lol[ii][1]
		z = lol[ii][2]
		i = lol[ii][3] - 1
		try:
			d[str([x, y])].append(i + 1)
		except:
			d[str([x, y])] = [i + 1]
		try:
			d1[x].append(i + 1)
		except:
			d1[x] = [i + 1]
	vis = [False] * n
	ans = []
	for i in d.values():
		if len(i) >= 2:
			for j in range(len(i) // 2):
				vis[i[j * 2] - 1] = True
				vis[i[j * 2 + 1] - 1] = True
				ans.append([i[j * 2], i[j * 2 + 1]])
	for i in d1.values():
		n1 = len(i)
		if n1 >= 2:
			j = 0
			k = 1
			while k < n1:
				if vis[i[j] - 1] == True:
					j += 1
				if vis[i[k] - 1] == True or j == k:
					k += 1
				if k < n1 and vis[i[k] - 1] == False and (vis[i[j] - 1] == False):
					ans.append([i[k], i[j]])
					vis[i[k] - 1] = True
					vis[i[j] - 1] = True
	i = 0
	j = 1
	c = 0
	while j < n:
		if vis[lol[i][3] - 1] == True:
			i += 1
		if vis[lol[j][3] - 1] == True or j == i:
			j += 1
		if j < n and vis[lol[i][3] - 1] == False and (vis[lol[j][3] - 1] == False):
			ans.append([lol[i][3], lol[j][3]])
			vis[lol[i][3] - 1] = True
			vis[lol[j][3] - 1] = True
	for i in ans:
		print(*i)
sync_with_stdio(False)
main()


def solve(n, p):
	p = sorted(p, key=lambda x: (x[0], x[1], x[2]))
	p.append([10 ** 20, 10 ** 20, 10 ** 20, 10 ** 20])
	c = 1
	pn = []
	for i in range(1, len(p)):
		if p[i][0] == p[i - 1][0]:
			c += 1
		else:
			if c >= 2:
				s = solve_2d(p[i - c:i])
				if s:
					pn.append(s)
			else:
				pn.append(p[i - 1])
			c = 1
	for i in range(0, len(pn) - 1, 2):
		print(pn[i][3], pn[i + 1][3])

def solve_2d(p1):
	p1.append([10 ** 20, 10 ** 20, 10 ** 20, 10 ** 20])
	c = 1
	p1n = []
	i = 1
	while i < len(p1):
		if p1[i][1] == p1[i - 1][1]:
			print(p1[i][3], p1[i - 1][3])
			i += 2
		else:
			p1n.append(p1[i - 1])
			i += 1
	for i in range(0, len(p1n) - 1, 2):
		print(p1n[i][3], p1n[i + 1][3])
	if len(p1n) % 2 == 1:
		return p1n[-1]
	else:
		return 0

def main():
	n = int(input())
	p = []
	for i in range(n):
		pt = [int(i) for i in input().split()]
		p.append(pt + [i + 1])
	solve(n, p)
main()


n = int(input())
coords = n * [-1]
coordsy = list()
coordsz = list()
for i in range(n):
	coords[i] = [int(i) for i in input().split()] + [i]
coords.sort()
i = 0
while i < len(coords) - 1:
	if coords[i][:2] == coords[i + 1][:2]:
		print(coords[i][3] + 1, coords[i + 1][3] + 1)
		i += 1
	else:
		coordsy.append(coords[i])
	i += 1
	if i == len(coords) - 1:
		coordsy.append(coords[i])
i = 0
while i < len(coordsy) - 1:
	if coordsy[i][:1] == coordsy[i + 1][:1]:
		print(coordsy[i][3] + 1, coordsy[i + 1][3] + 1)
		i += 1
	else:
		coordsz.append(coordsy[i])
	i += 1
	if i == len(coordsy) - 1:
		coordsz.append(coordsy[i])
for i in range(0, len(coordsz), 2):
	print(coordsz[i][3] + 1, coordsz[i + 1][3] + 1)


def solve(n, points):
	points = [p + (i,) for (i, p) in enumerate(points, 1)]
	points += [(10 ** 9,) * 3]
	points.sort()
	ans = []
	rem = []
	i = 0
	while i < n:
		if points[i][:2] == points[i + 1][:2]:
			ans.append((points[i][-1], points[i + 1][-1]))
			i += 2
		else:
			rem.append(i)
			i += 1
	rem += [n]
	rem2 = []
	n = len(rem)
	i = 0
	while i < n - 1:
		if points[rem[i]][0] == points[rem[i + 1]][0]:
			ans.append((points[rem[i]][-1], points[rem[i + 1]][-1]))
			i += 2
		else:
			rem2.append(points[rem[i]][-1])
			i += 1
	for e in ans:
		print(*e)
	for i in range(0, len(rem2), 2):
		print(rem2[i], rem2[i + 1])

def main():
	n = int(input())
	points = [tuple((int(c) for c in input().split())) for _ in range(n)]
	solve(n, points)
main()


from collections import defaultdict

def main():
	points = []
	n = int(input())
	z_to_xy = defaultdict(lambda : [])
	for i in range(n):
		(x, y, z) = [int(x) for x in input().split()]
		points.append([x, y, z, i])
		z_to_xy[z].append([x, y, i])
	rem_global = []
	for z in z_to_xy:
		y_to_x = defaultdict(lambda : [])
		for p in z_to_xy[z]:
			y_to_x[p[1]].append([p[0], p[2]])
		rem = []
		for y in y_to_x:
			temp = sorted(y_to_x[y])
			i = 0
			while i < len(temp) - 1:
				print(temp[i][1] + 1, temp[i + 1][1] + 1)
				i += 2
			if i == len(temp) - 1:
				rem.append([y, temp[i][0], temp[i][1]])
		temp2 = sorted(rem)
		i = 0
		while i < len(temp2) - 1:
			print(temp2[i][-1] + 1, temp2[i + 1][-1] + 1)
			i += 2
		if i == len(temp2) - 1:
			rem_global.append([z, temp2[i][1], temp2[i][0], temp2[i][-1]])
	temp = sorted(rem_global)
	i = 0
	while i < len(temp) - 1:
		print(temp[i][-1] + 1, temp[i + 1][-1] + 1)
		i += 2
py2 = round(0.5)
if py2:
	from future_builtins import ascii, filter, hex, map, oct, zip
	range = xrange
import os, sys
from io import IOBase, BytesIO
BUFSIZE = 8192

class FastIO(BytesIO):
	newlines = 0

	def __init__(self, file):
		self._file = file
		self._fd = file.fileno()
		self.writable = 'x' in file.mode or 'w' in file.mode
		self.write = super(FastIO, self).write if self.writable else None

	def _fill(self):
		s = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
		self.seek((self.tell(), self.seek(0, 2), super(FastIO, self).write(s))[0])
		return s

	def read(self):
		while self._fill():
			pass
		return super(FastIO, self).read()

	def readline(self):
		while self.newlines == 0:
			s = self._fill()
			self.newlines = s.count(b'\n') + (not s)
		self.newlines -= 1
		return super(FastIO, self).readline()

	def flush(self):
		if self.writable:
			os.write(self._fd, self.getvalue())
			(self.truncate(0), self.seek(0))

class IOWrapper(IOBase):

	def __init__(self, file):
		self.buffer = FastIO(file)
		self.flush = self.buffer.flush
		self.writable = self.buffer.writable
		if py2:
			self.write = self.buffer.write
			self.read = self.buffer.read
			self.readline = self.buffer.readline
		else:
			self.write = lambda s: self.buffer.write(s.encode('ascii'))
			self.read = lambda : self.buffer.read().decode('ascii')
			self.readline = lambda : self.buffer.readline().decode('ascii')
(sys.stdin, sys.stdout) = (IOWrapper(sys.stdin), IOWrapper(sys.stdout))
input = lambda : sys.stdin.readline().rstrip('\r\n')
main()


def solve(n, points):
	for i in range(n):
		points[i].append(i + 1)
	points.sort()
	points += [(float('inf'),) * 3]
	rem = []
	i = 0
	while i < n:
		if points[i][:2] == points[i + 1][:2]:
			print(points[i][3], points[i + 1][3])
			i += 2
		else:
			rem.append(i)
			i += 1
	rem.append(n)
	rem2 = []
	i = 0
	while i < len(rem) - 1:
		if points[rem[i]][0] == points[rem[i + 1]][0]:
			print(points[rem[i]][3], points[rem[i + 1]][3])
			i += 2
		else:
			rem2.append(points[rem[i]][3])
			i += 1
	for i in range(0, len(rem2), 2):
		print(rem2[i], rem2[i + 1])

def main():
	n = int(input())
	points = [[int(c) for c in input().split()] for _ in range(n)]
	solve(n, points)
main()


import sys
input = sys.stdin.readline
n = int(input())
P = [list(map(int, input().split())) + [i + 1] for i in range(n)]
P.sort(reverse=True)
P2 = []
while P:
	(x, y, z, w) = P.pop()
	if len(P) > 0 and x == P[-1][0] and (y == P[-1][1]):
		(x2, y2, z2, w2) = P.pop()
		print(w, w2)
	else:
		P2.append((x, y, z, w))
P = P2
P.sort(reverse=True)
P2 = []
while P:
	(x, y, z, w) = P.pop()
	if len(P) > 0 and x == P[-1][0]:
		(x2, y2, z2, w2) = P.pop()
		print(w, w2)
	else:
		P2.append((x, y, z, w))
P = P2
for i in range(0, len(P), 2):
	print(P[i][3], P[i + 1][3])


def solve(n, points):
	points = sorted((p + (i,) for (i, p) in enumerate(points, 1)))
	points += [(float('inf'),) * 3]
	rem = []
	i = 0
	while i < n:
		if points[i][:2] == points[i + 1][:2]:
			print(points[i][3], points[i + 1][3])
			i += 2
		else:
			rem.append(i)
			i += 1
	rem.append(n)
	rem2 = []
	i = 0
	while i < len(rem) - 1:
		if points[rem[i]][0] == points[rem[i + 1]][0]:
			print(points[rem[i]][3], points[rem[i + 1]][3])
			i += 2
		else:
			rem2.append(points[rem[i]][3])
			i += 1
	for i in range(0, len(rem2), 2):
		print(rem2[i], rem2[i + 1])

def main():
	n = int(input())
	points = [tuple((int(c) for c in input().split())) for _ in range(n)]
	solve(n, points)
main()


n = int(input())
a = [[]]
for i in range(n):
	(x, y, z) = map(int, input().split())
	a.append([x, y, z])
from collections import defaultdict

def solve(lst, k):
	if k == 3:
		return lst[0]
	mp = defaultdict(list)
	for i in lst:
		mp[a[i][k]].append(i)
	ans = []
	p = []
	for i in mp:
		p.append(i)
	p.sort()
	for i in p:
		t = solve(mp[i], k + 1)
		if t != -1:
			ans.append(t)
	for i in range(0, len(ans) - 1, 2):
		print(ans[i], ans[i + 1])
	if len(ans) % 2:
		return ans[-1]
	return -1
solve([i for i in range(1, n + 1)], 0)


n = int(input())
coors = []
for i in range(n):
	coors.append(list(map(int, input().split())) + [i + 1])
coors = sorted(coors, key=lambda x: (x[0], x[1], x[2]))
left = []

def oneD(co, remain):
	if len(co) % 2 == 0:
		for i in range(0, len(co), 2):
			print(co[i][3], co[i + 1][3])
	else:
		remain.append(co[-1])
		for i in range(0, len(co) - 1, 2):
			print(co[i][3], co[i + 1][3])
	return remain

def twoD(co):
	if len(co) == 1:
		left.append(*co)
		return
	remain = []
	l = 1
	for i in range(len(co) - 1):
		if co[i][1] == co[i + 1][1]:
			l += 1
		else:
			remain = oneD(co[i + 1 - l:i + 1], remain)
			l = 1
	remain = oneD(co[len(co) - l:], remain)
	if len(remain) % 2 == 0:
		for i in range(0, len(remain), 2):
			print(remain[i][3], remain[i + 1][3])
	else:
		left.append(remain[-1])
		for i in range(0, len(remain) - 1, 2):
			print(remain[i][3], remain[i + 1][3])
l = 1
for i in range(n - 1):
	if coors[i][0] == coors[i + 1][0]:
		l += 1
	else:
		twoD(coors[i + 1 - l:i + 1])
		l = 1
twoD(coors[n - l:])
for i in range(0, len(left), 2):
	print(left[i][3], left[i + 1][3])


n = int(input())
points = []
for i in range(n):
	(x, y, z) = map(int, input().split())
	points.append((x, y, z, i + 1))
points.sort()
x_points = {}
for p in points:
	(x, y, z, i) = p
	if x in x_points:
		x_points[x].append(p)
	else:
		x_points[x] = [p]
x_to_remove = []
for (x, pp) in x_points.items():
	if len(pp) >= 2:
		y_points = {}
		for p in pp:
			(x, y, z, i) = p
			if y in y_points:
				y_points[y].append(p)
			else:
				y_points[y] = [p]
		y_to_remove = []
		for (y, ppp) in y_points.items():
			if len(ppp) >= 2:
				ppp.sort()
				for i in range(0, len(ppp) - 1, 2):
					print(ppp[i][3], ppp[i + 1][3])
				if len(ppp) % 2:
					y_points[y] = [ppp[-1]]
				else:
					y_to_remove.append(y)
		for y in y_to_remove:
			del y_points[y]
		indexes = [(ppp[0][3], y) for (y, ppp) in sorted(y_points.items())]
		for i in range(0, len(indexes) - 1, 2):
			print(indexes[i][0], indexes[i + 1][0])
		if len(indexes) % 2:
			x_points[x] = y_points[indexes[-1][1]]
		else:
			x_to_remove.append(x)
for x in x_to_remove:
	del x_points[x]
indexes = [pp[0][3] for (x, pp) in sorted(x_points.items())]
for i in range(0, len(indexes), 2):
	print(indexes[i], indexes[i + 1])


import sys
n = int(input())
d = [tuple([int(i) for i in sys.stdin.readline().split()]) for j in range(n)]
index = {}
for i in range(n):
	index[d[i]] = i + 1
d.sort()
untaken = []
dic = {}
i = 0
while i < n:
	first = d[i][0]
	if first not in dic:
		dic[first] = []
	dic[first].append((d[i][1], d[i][2]))
	i += 1
for dd in dic:
	e = dic[dd]
	nn = len(e)
	unt = []
	i = 0
	while i < nn:
		if i < nn - 1 and e[i][0] == e[i + 1][0]:
			sys.stdout.write(str(index[(dd,) + e[i]]) + ' ' + str(index[(dd,) + e[i + 1]]) + '\n')
			i += 2
		else:
			unt.append(i)
			i += 1
	for j in range(0, len(unt) - 1, 2):
		sys.stdout.write(str(index[(dd,) + e[unt[j]]]) + ' ' + str(index[(dd,) + e[unt[j + 1]]]) + '\n')
	if len(unt) & 1:
		untaken.append((dd,) + e[unt[-1]])
for i in range(0, len(untaken), 2):
	sys.stdout.write(str(index[untaken[i]]) + ' ' + str(index[untaken[i + 1]]) + '\n')