from time import time
st=time()

import sys
input = lambda: sys.stdin.readline().rstrip()
from math import log10,exp
from copy import copy,deepcopy
from random import randint,random,choice
from bisect import bisect,bisect_left,insort



MAX_OP=50
FIRST_PHASE=0.2
TIME_LIMIT=0.9
TARGET_NUM=5*10**17

# カード1のスコアだけ見ればいいのか
# 奇数回目の操作でカード1以外を操作する
# 偶数回目でカード1を操作する

# カード1のスコアを計算

def calc_front():return abs(tempAB[0][0]-TARGET_NUM)

def calc_back():return abs(tempAB[0][1]-TARGET_NUM)

def calc_Score(cnt):
    V1=calc_front()
    V2=calc_front()
    
    temp=max(V1,V2)

    if temp==0:return 2000050-cnt
    return int(2000000-100000*log10(temp+1))

# 二枚のカードの表裏の平均値を返す
def calc_ave(u,v):

    retf=(tempAB[u][0]+tempAB[v][0])//2
    retb=(tempAB[u][1]+tempAB[v][1])//2

    return retf,retb

def rewrite(u,v):
    tempf,tempb=calc_ave(u,v)
    tempAB[u][0]=tempf
    tempAB[v][0]=tempf

    tempAB[u][1]=tempb
    tempAB[v][1]=tempb


def Judge(N,AB,X,UV):
    def WrongAnswer(str):
        print("Wrong Answer (" + str + ")")
        sys.exit(0)

    # Step 1. テストケースの入力を受け取る

    A = [0] * (N + 1)
    B = [0] * (N + 1)
    for i in range(1, N+1):
        A[i], B[i] = AB[i-1]

    # Step 2. あなたの出力を受け取る
    if X < 0 or X > 50:
        WrongAnswer("X is out of range")

    U = [0] * (X + 1)
    V = [0] * (X + 1)
    for i in range(1, X+1):
        U[i], V[i] = UV[i-1]
        if U[i] == V[i]:
            WrongAnswer("U[i] and V[i] are same")
        elif U[i] < 1 or U[i] > N:
            WrongAnswer("U[i] is out of range")
        elif V[i] < 1 or V[i] > N:
            WrongAnswer("V[i] is out of range")

    # Step 3. シミュレーションを行う
    for i in range(1, X+1):
        avgA = (A[U[i]] + A[V[i]]) // 2
        avgB = (B[U[i]] + B[V[i]]) // 2
        A[U[i]] = avgA
        A[V[i]] = avgA
        B[U[i]] = avgB
        B[V[i]] = avgB

    # Step 4. 出力
    ErrorA = abs(500000000000000000 - A[1])
    ErrorB = abs(500000000000000000 - B[1])
    Score = (int)(2000000.0 - 100000.0 * log10(1.0 * max(ErrorA, ErrorB) + 1.0))
    if ErrorA == 0 and ErrorB == 0:
        Score = 2000050 - X
    print("Accepted!")
    print("Error of A[1] = " + str(ErrorA))
    print("Error of B[1] = " + str(ErrorB))
    print("Score = " + str(Score))

N=int(input())
AB=[list(map(int, input().split()))  for _ in range(N)]


NowScore=0
UV=[]

while time()-st<=TIME_LIMIT:

    tempAB=deepcopy(AB)    
    tempUV=[]
    preop=-1

    opcnt=randint(0,MAX_OP)

    # 奇数回目は1にマッチさせるものを選ぶ
    # 偶数回目で1とマッチさせる
    for cnt in range(1,opcnt+1):

        if cnt&1:
            tarf=2*TARGET_NUM-tempAB[0][0]
            tarb=2*TARGET_NUM-tempAB[0][1]

            preScore=10**20

            u,v=-1,-1
            # 適当にu,vの平均を計算してaとマッチさせられるか考える
            for _ in range(20):
                tu=randint(1,N-1)
                tv=randint(1,N-1)
                while tu==tv:tv=randint(0,N-1)

                tf,tb=calc_ave(tu,tv)
                temp=abs(tf-tarf)+abs(tb-tarb)
                if temp<preScore:
                    preScore=temp
                    u=tu
                    v=tv


            rewrite(u,v)
            tempUV.append((u+1,v+1))
            preop=u

        else:
            # 1とさっき計算したものをマッチさせる
            rewrite(0,preop)
            tempUV.append((1,preop+1))


    tempScore=calc_Score(opcnt)

    if tempScore>NowScore:
        NowScore=tempScore
        UV=deepcopy(tempUV)

    # else:
    #     T=(time()-st)/TIME_LIMIT
    #     if exp((tempScore-NowScore)/T)>random():
    #         NowScore=tempScore
    #         UV=deepcopy(tempUV)


print(len(UV))
for u,v in UV:print(u,v)