N = int(input())
if N <= 2:
  print(-1)
else: 
  M = 2 * N ** 2
  print(M)
  for i in range(N ** 2):
    print(f"{i % (N*N) + 1} {(i+2) % (N*N) + 1}")
  for i in range(N ** 2):
    print(f"{i % (N*N) + 1} {(i+4) % (N*N) + 1}")