import sys
input = sys.stdin.readline

N=int(input())

if N%2==0:
    print(-1)
else:
    ANS=set()

    for i in range(1,N*N+1):
        for j in [i-1,i-2,i+1,i+2]:
            if j>N*N:
                j-=N*N
            if j<=0:
                j+=N*N
            X=[i,j]
            X.sort()
            ANS.add(tuple(X))

    print(len(ANS))

    for x,y in ANS:
        print(x,y)