from math import log10, floor, exp
from random import randint, random
from time import time

time_start = time()

N = int(input())
init_A, init_B = [list(i) for i in zip(*[list(map(int, input().split())) for _ in range(N)])]

def calc_socre(op):
    A, B = exec_op(op)
    X = len(op)

    V1, V2 = abs(5*10**17-A[0]), abs(5*10**17-B[0])
    V = max(V1, V2)
    if V == 0:
        return 2000050 - X
    else:
        return floor(2000000.0 - 100000.0 * log10(V+1))

def exec_op(op):
    A, B = init_A[:], init_B[:]
    for u, v in op:
        a, b = A[u-1], A[v-1]
        A[u-1], A[v-1] = (a+b)//2, (a+b)//2
        c, d = B[u-1], B[v-1]
        B[u-1], B[v-1] = (c+d)//2, (c+d)//2
    return A, B

X = 50
op = []
A, B = init_A[:], init_B[:]
while len(op) < X//2:
    min_A, max_A = min(A), max(A)
    u, v = A.index(min_A), A.index(max_A)
    if u == v:
        break
    op.append((u+1, v+1))
    A[u], A[v] = (min_A+max_A)//2, (min_A+max_A)//2

while len(op) < X:
    min_B, max_B = min(B), max(B)
    u, v = B.index(min_B), B.index(max_B)
    if u == v:
        break
    op.append((u+1, v+1))
    B[u], B[v] = (min_B+max_B)//2, (min_B+max_B)//2

while len(op) < X:
    u, v = randint(1, N), randint(1, N)
    if u == v:
        continue
    op.append((u, v))


# 山登り法
# score = calc_socre(op)
# while time() - time_start < 0.90:
#     if randint(0, 1):
#         u = randint(1, N-1)
#         v = randint(u+1, N)
#         op[randint(0, X-1)] = (u, v)
#     else:
#         u, v = randint(0, X-1), randint(0, X-1)
#         op[u], op[v] = op[v], op[u]
#     new_score = calc_socre(op)
#     if new_score > score:
#         score = new_score
#     else:
#         op[u], op[v] = op[v], op[u]
    
# 焼きなまし
score = calc_socre(op)
start_temp = 2000
end_temp = 10
TIME_LIMIT = 0.90

while True:
    now_time = time() - time_start
    if now_time > TIME_LIMIT:
        break
    new_op = op[:]
    if randint(0, 1):
        u = randint(1, N-1)
        v = randint(u+1, N)
        new_op[randint(0, X-1)] = (u, v)
    else:
        u, v = randint(0, X-1), randint(0, X-1)
        new_op[u], new_op[v] = new_op[v], new_op[u]
    new_score = calc_socre(new_op)
    temp = start_temp + (end_temp - start_temp) * now_time / TIME_LIMIT
    prob = exp(min(0, (new_score - score) / temp))
    if new_score > score or random() < prob:
        op = new_op
        score = new_score

# print(score)

print(X)
for u, v in op:
    print(u, v)