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, b, c, d = randrange(1, N2), randrange(1, N2), randrange(1, N2), randrange(1, N2)
    if len(set([a, b, c, d])) < 4:
        continue
    if (a+b+c+d)%N2 != 0:
        continue
    edge = []
    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))

    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)
        for u, v in edge:
            if u < v:
                print(u, v)
        break