题解 | #火车进站#

import sys

num1=int(input())
rulie=input().split()        #入列
rulie=rulie[::-1]
stack=''                      #栈中
chulie=''                     #出列
fangan=[]
def guocheng(rulie,stack,chulie):
    if rulie:
        guocheng(rulie[0:-1],stack+rulie[-1],chulie)
    if stack:
        guocheng(rulie,stack[0:-1],chulie+stack[-1])
    if len(chulie)==num1:
        fangan.append(chulie)
        return
    
guocheng(rulie,stack,chulie)
fangan=sorted(fangan)
for i in fangan:
    print(' '.join(i))