import sys
sys.setrecursionlimit(3000)
def dfs(n, start, mid, end):
if n > 0:
dfs(n-1, start, end, mid)
print(start, end)
dfs(n-1, mid, start, end)
n = int(input())
print(2**n -1)
if n > 20:
sys.exit()
dfs(n,1,2,3)