N = int(input())
if N < 3:
  print(-1)
else: 
  M = 2 * N ** 2
  print(M)
  for i in range(1,N ** 2):
    print(f"{i} {i + 1}")
  print(f"{N ** 2} {1}")
  for i in range(1,N**2 + 1):
    print(f"{i} {i}")
    print(f"{i} {i}")