N = int(input())
if N <= 2:
    print(-1)
    exit()
print(4*N**2//2)

base = [2,3,4,5]
need = (2*N**2+4)-14
tmp = need//4
for i in range(4):
    base[i] += tmp
need -= tmp*4
#print(need,base)
for i in range(need):
    base[~i] += 1
#print(base)
edge = set([])
t = 0
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
for i,j in edge:
    print(i,j)
#print(len(edge))