m = 430
n = 1 + m + m * (m - 1)
v = 2
e = []
for i in range(m):
    e.append((1, v))
    p = v
    v += 1
    for _ in range(m - 1):
        e.append((p, v))
        v += 1
assert len(e) == n - 1
print(n)
for u, v in e:
    print(u, v)