# 適当な例が答えだった
N = int(input())
if(N <= 2):
    print(-1)
else:
    print(N * N * 2)
    d = [-N, -1, 1, N]
    for i in range(N * N):
        for j in range(4):
            p = i + 1
            q = (i + d[j]) % (N * N) + 1
            if(p < q):
                print(p, q)