Best Cow Line

Best Cow Line

Time Limit: 1000MS

Memory Limit: 65536K

Description

FJ is about to take his N (1 ≤ N ≤ 2,000) cows to the annual"Farmer of the Year" competition. In this contest every farmer arranges his cows in a line and herds them past the judges.

The contest organizers adopted a new registration scheme this year: simply register the initial letter of every cow in the order they will appear (i.e., If FJ takes Bessie, Sylvia, and Dora in that order he just registers BSD). After the registration phase ends, every group is judged in increasing lexicographic order according to the string of the initials of the cows' names.

FJ is very busy this year and has to hurry back to his farm, so he wants to be judged as early as possible. He decides to rearrange his cows, who have already lined up, before registering them.

FJ marks a location for a new line of the competing cows. He then proceeds to marshal the cows from the old line to the new one by repeatedly sending either the first or last cow in the (remainder of the) original line to the end of the new line. When he's finished, FJ takes his cows for registration in this new order.

Given the initial order of his cows, determine the least lexicographic string of initials he can make this way.

Input

* Line 1: A single integer: N
* Lines 2..N+1: Line i+1 contains a single initial ('A'..'Z') of the cow in the ith position in the original line

Output

The least lexicographic string he can make. Every line (except perhaps the last one) contains the initials of 80 cows ('A'..'Z') in the new line.

Sample Input

6
A
C
D
B
C
B

Sample Output

ABCBCD

 

徐不可说：这道题大意为对字符串执行如下操作：从一个字符串头或尾删除一个字符，加到另外数组的尾部。重复多次操作构造出字典序尽可能小的的字符串。程序实现过程可简单设计为比较、删除、输出、再重复操作。但是，与之同时我们可以很容易得出本题一个逻辑，即当原字符串执行操作到首末字符相同时该如何删除？是删除第一个还是最后一个字符？由于字典序的不同，这应该取决于假设已删除这个字符比较下一个字符的大小。关键在于如何实现这个逻辑，下面我给出的代码使用了循环的方法。