"""
0 1
2 3

0 1 2
3 4 5
6 7 8

"""

def solve(n):
    for i in range(n):
        for j in range(n):
            z = 0
            for dx, dy in [[1, 0], [0, 1], [-1, 0], [0, -1]]:
                nx = (i + dx) % n
                ny = (j + dy) % n
                z += nx * n + ny
            if (z - (i * n + j) * 4) % (n * n) != 0:
                # print(i, j, (z - (i * n + j) * 4) % (n * n))
                return False
    return True
n = int(input())

if n <= 2:
    print(-1)
else:
    sum = [0] * (n * n)
    deg = [0] * (n * n)
    for i in range(n * n):
        for dx in [-n, -1, 1, n]:
            j = (i + dx) % (n * n)
            sum[j] += i
            deg[i] += 1
    assert all(deg[i] == 4 for i in range(n * n)) and all((sum[i] - i * 4) % (n * n) == 0 for i in range(n * n))

    print(n * n * 2)
    for i in range(n * n):
        for dx in [1, n]:
            j = (i + dx) % (n * n)
            print(i + 1, j + 1)