from math import log10, floor
from random import randint
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 = []
for _ in range(X):
    u = randint(1, N-1)
    v = randint(u+1, N)
    op.append((u, v))

# 山登り法
score = calc_socre(op)
while time() - time_start < 0.90:
    # 確率0.5で一点変異
    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]

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