from collections import deque
from random import randrange

N = int(input())

if N == 1 or N == 2:
    exit(print(-1))

def MOD1(a):
    while N2 < a:
        a -= N2
    return a

N2 = N**2
while True:
    a = randrange(1, N2-3)
    b = a+1
    c = randrange(b+1, N2-1)
    d = c+1
    if (a+b+c+d)%N2 != 0:
        continue
    edge = []
    S = set()
    cnt = [0]*N2
    for i in range(1, N2+1):
        E = [i+a, i+b, i+c, i+d]
        for j in range(4):
            E[j] = MOD1(E[j])
        for e in E:
            edge.append((i, e))
            if (e, i) not in S:
                S.add((i, e))
                cnt[i-1] += 1
                cnt[e-1] += 1
    if cnt.count(4) < N2:
        continue

    G = [[] for _ in range(N2)]
    for u, v in edge:
        u, v = u-1, v-1
        G[u].append(v)
    visited = [-1]*N2
    visited[0] = 0
    que = deque()
    que.append(0)
    while que:
        n = que.popleft()
        for v in G[n]:
            if visited[v] == -1:
                visited[v] = visited[n]+1
                que.append(v)

    if max(visited) <= N:
        print(len(edge)//2)
        S = set()
        for u, v in edge:
            u, v = u-1, v-1
            if (v, u) not in S:
                print(u+1, v+1)
                S.add((u, v))
        break