#!/usr/bin/pypy3

from collections import deque

N = 199993
L = 39999

G = [[] for i in range(N + 1)]
p = 6000

for i in range(1, L):
    G[i].append(i + 1)
    G[i + 1].append(i)

id = L + 1

for u in range(1, L + 1):
    now = u

    if u == p: # 縦に 3 つ
        G[now].append(id)
        G[id].append(now)
        id += 1
        G[now].append(id)
        G[id].append(now)
        id += 1
    else:  # 縦に 5 つ
        G[now].append(id)
        G[id].append(now)
        now = id
        id += 1
        G[now].append(id)
        G[id].append(now)
        id += 1

        now = u
        G[now].append(id)
        G[id].append(now)
        now = id
        id += 1
        G[now].append(id)
        G[id].append(now)
        id += 1

S = deque()
S.append(1)
visited = [False] * (N + 1)

print(N)

while len(S) > 0:
    now = S.pop()
    visited[now] = True

    for nx in G[now]:
        if visited[nx]:
          continue
        print(min(now, nx), max(now, nx))
        S.append(nx)