N = int(input())

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

def f(x):
    array = []
    array.append((x+1)%(N**2))
    array.append((x-1)%(N**2))
    array.append((x+N)%(N**2))
    array.append((x-N)%(N**2))
    return array


print(2*N**2)
for i in range(N**2):
    for j in f(i):
        i = i if i != 0 else N**2
        j = j if j != 0 else N**2
        if i < j:
            print(i,j)