H = 1
last = 1

ret = []
for _ in range(2000):
    ret.append((H, last + 1))
    ret.append((last + 1, last + 2))
    ret.append((last + 2, last + 3))
    ret.append((last + 3, last + 4))
    H = last + 2
    last += 4

print(len(ret))
for a, b in ret:
    print(a, b)