E = []
n = 190000
x = 1
while len(E) < n:
    E.append((x, x + 1))
    E.append((x + 1, x + 2))
    E.append((x, x + 3))
    E.append((x + 3, x + 4))
    x += 4
E.append((x - 1, x + 1))
x += 1

n = x
print(n)
for u, v in E:
    print(u, v)