from time import time
start = time()
import sys,math
if len(sys.argv) == 2: sys.stdin = open(sys.argv[1])
from random import randint,randrange,sample,shuffle,choice
from collections import defaultdict,deque
from itertools import combinations,permutations,accumulate,product
from bisect import bisect,bisect_left,bisect_right
from heapq import heappop,heappush,heapify
from copy import deepcopy
def input(): return sys.stdin.readline().rstrip()
def ii(): return int(input())
def ms(): return map(int, input().split())
def li(): return list(map(int,input().split()))
# ////////////////////////////////
N = ii()
A = list()
B = list()
for i in range(N):
  a,b = ms()
  A.append([a,i])
  B.append([b,i])
NUM = [i for i in range(2,N)]
STAND = 5*pow(10,17)
TURN = 0
V1,V2 = abs(A[0][0]-STAND),abs(B[0][0]-STAND)
def create_abs():
  ABS = list()
  for v in range(1,N):
    na,nb = (A[0][0]+A[v][0])//2,(B[0][0]+B[v][0])//2
    n1,n2 = abs(na-STAND),abs(nb-STAND)
    tmp = max(V1,V2)-max(n1,n2)
    ABS.append((tmp,v))
  ABS.sort(reverse=True)
  return ABS

def other_merge(): # STANDにできるだけ近いやつを作る
  CAND = list()
  for (u,v) in combinations(NUM,2):
    na,nb = (A[u][0]+A[v][0])//2,(B[u][0]+B[v][0])//2
    n1,n2 = abs(na-STAND),abs(nb-STAND)
    CAND.append((max(n1,n2),u,v))
  CAND.sort()
  u,v = CAND[0][1],CAND[0][2]
  return u,v


ANS = list()
while TURN<50:
  if time()-start>2.85: break
  ABS = create_abs()
  if ABS[0][0]==0: # 頭打ちになったら1以外とマージする
    u,v = other_merge()
  else:
    u,v = 0,ABS[0][1]
  ANS.append((u+1,v+1))
  na,nb = (A[u][0]+A[v][0])//2,(B[u][0]+B[v][0])//2
  if u==0:
    n1,n2 = abs(na-STAND),abs(nb-STAND)
    V1,V2 = n1,n2
  A[u][0],A[v][0],B[u][0],B[v][0] = na,na,nb,nb
  TURN += 1
  
print(len(ANS))
for u,v in ANS: print(u,v)