N = int(input())
if N <= 2:
    print(-1)
    exit()

base = [N+1,N**2-N+1,N+2,N**2-N]
edge = set([])
t = 0
#print(base)
for i in range(1,N**2+1):
    for j in base:
        a = i
        if j+t > N**2:
            b = (j+t)%N**2
        else:
            b = j+t
        if a > b:
            a,b = b,a
        edge.add((a,b))
    
    t += 1
cnt = [0] * N**2
c_sum = [0] * N**2
print(len(edge))
for i,j in edge:
    print(i,j)
    cnt[i-1] += 1
    cnt[j-1] += 1
    c_sum[i-1] += j
    c_sum[i-1] %= N**2
    c_sum[j-1] += i
    c_sum[j-1] %= N**2
#print(cnt)
#print(edge)
#print(c_sum)
#print([4*i%(N**2) for i in range(1,N**2+1)])
#print(c_sum == [4*i%(N**2) for i in range(1,N**2+1)])