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