from time import time
start_time = time()

import sys
import io, os
input = sys.stdin.readline
#input = io.BytesIO(os.read(0,os.fstat(0).st_size)).readline

import math
import random
random.seed(42)

m = 50
TIME_LIMIT = 0.85
L = 5*10**17

start_temp = 10**14
end_temp = 1000

def move_element(lst, i, j):
    lst_ = lst.copy()
    element = lst_.pop(i)
    lst_.insert(j, element)
    return lst_

n =  int(input())
A = [0]*n
B = [0]*n
for i in range(n):
    a, b = map(int, input().split())
    A[i] = a
    B[i] = b

ans = []
for i in range(m-1):
    u, v = random.sample(range(n), 2)
    ans.append((u, v))
v = random.randint(1, n-1)
ans.append((0, v))

def calc_score(ans):
    Ac = A.copy()
    Bc = B.copy()
    for u, v in ans:
        x = (Ac[u]+Ac[v])//2
        Ac[u], Ac[v] = x, x
        y = (Bc[u]+Bc[v])//2
        Bc[u], Bc[v] = y, y
    v1 = abs(L-Ac[0])
    v2 = abs(L-Bc[0])
    cost = max(v1, v2)
    return cost

cost = calc_score(ans)
best_cost = cost
best_ans = ans.copy()
iter = 0
while True:
    iter += 1
    now_time = time()
    if now_time - start_time > TIME_LIMIT:
        break
    neigh = neigh = random.randint(0, 1)
    if neigh == 0:
        # ランダムに1操作を選んで変更する
        i = random.randint(0, m-1)
        if i != m-1:
            idx = random.randint(0, 1)
            u = ans[i][idx]
            while True:
                v = random.randint(0, n-1)
                if v == u:
                    continue
                break
        else:
            v = random.randint(1, n-1)
            u = 0
        pre = ans[i]
        ans[i] = (u, v)
        new_cost = calc_score(ans)
        if new_cost <= best_cost:
            best_cost = new_cost
            best_ans = ans.copy()
        temp = start_temp+(end_temp-start_temp)*(now_time-start_time)/TIME_LIMIT
        if new_cost <= cost:
            prob = 1
        else:
            #prob = math.exp((cost-new_cost)/temp)
            prob = 0
        if prob > random.random():
            cost = new_cost
        else:
            ans[i] = pre
    else:
        # ランダムに1操作の位置を変更する
        i = random.randint(0, m-2)
        j = random.randint(0, m-2)
        new_ans = move_element(ans, i, j)
        new_cost = calc_score(new_ans)
        if new_cost <= best_cost:
            best_cost = new_cost
            best_ans = ans.copy()
        temp = start_temp+(end_temp-start_temp)*(now_time-start_time)/TIME_LIMIT
        if new_cost <= cost:
            prob = 1
        else:
            #prob = math.exp((cost-new_cost)/temp)
            prob = 0
        if prob > random.random():
            cost = new_cost
            ans = new_ans.copy()

print(len(best_ans))
for i in range(len(best_ans)):
    u, v = best_ans[i]
    u, v = u+1, v+1
    print(u, v)

if cost != 0:
    score = (int)(2000000-100000*math.log10(best_cost+1))
else:
    score = 2000050-len(best_ans)
print(cost, file=sys.stderr)
print(iter, file=sys.stderr)
print(score, file=sys.stderr)