dxdy = ((0, 1), (-1, 0))
n = int(input())
if n <= 2:
    print(-1)
    exit(0)
ans = []
for i in range(n):
    for j in range(n):
        t = i * n + j
        for dx, dy in dxdy:
            t2 = ((i + dx) * n + (j + dy)) % (n * n)
            ans.append((t, t2))
print(len(ans))
for x, y in ans:
    print(x + 1, y + 1)