N = int(input())
cnt = [i for i in range(2*N)]
ans = []
def dfs(i,List):
    global cnt
    global ans
    if i == N-1:
        flag2 = True
        flag1 = True
        S = []
        for s in List:
            if cnt[s] >= 2:
                pass
            elif cnt[s] == 1:
                flag2 = False
            else:
                flag2 = False
                flag1 = False
        if flag2:
            for s in List:
                cnt[s]-=2
                S.append(s)
            ans.append(S)
            ans.append(S)

        elif flag1:
            for s in List:
                cnt[s]-=1
                S.append(s)
            ans.append(S)
    else:
        for nx in range(List[i]-1,0,-1):
            dfs(i+1,List + [nx])
for l in range(2*N-1,1,-1):
    dfs(0,[l])
print(len(ans))
for s in ans:
    print(*s)