Problem Statement

Given is a string s of length N.
Let s_i denote the i-th character of s.
Snuke will transform s by the following procedure.

• Choose an even length (not necessarily contiguous) subsequence $x=(x_1, x_2, \ldots, x_{2k})$ of $(1,2, \ldots, N) (k$ may be 0).
• Swap s_{x_1} and s_{x_{2k}}.
• Swap s_{x_2} and s_{x_{2k-1}}.
• Swap s_{x_3} and s_{x_{2k-2}}.
• $\vdots$
• Swap s_{x_{k}} and s_{x_{k+1}}.

Among the strings that s can become after the procedure, find the lexicographically smallest one.

What is the lexicographical order?

Simply speaking, the lexicographical order is the order in which words are listed in a dictionary. As a more formal definition, here is the algorithm to determine the lexicographical order between different strings S and T.

Below, let S_i denote the i-th character of S. Also, if S is lexicographically smaller than T, we will denote that fact as $S \lt T$; if S is lexicographically larger than T, we will denote that fact as $S \gt T$.

• Let L be the smaller of the lengths of S and T. For each $i=1,2,\dots,L$, we check whether S_i and T_i are the same.

• If there is an i such that $S_i \neq T_i$, let j be the smallest such i. Then, we compare S_j and T_j. If S_j comes earlier than T_j in alphabetical order, we determine that $S \lt T$ and quit; if S_j comes later than T_j, we determine that $S \gt T$ and quit.

• If there is no i such that $S_i \neq T_i$, we compare the lengths of S and T. If S is shorter than T, we determine that $S \lt T$ and quit; if S is longer than T, we determine that $S \gt T$ and quit.

Input

Input is given from Standard Input in the following format:
N
s

Output

Print the lexicographically smallest possible string s after the procedure by Snuke.

Constraints

• $1 \leq N \leq 2 \times 10^5$
• s is a string of length N consisting of lowercase English letters.

Sample Input 1

4
dcab

Sample Output 1

acdb

• When x=(1,3), the procedure just swaps s_{1} and s_{3}.
• The s after the procedure is acdb, the lexicographically smallest possible result.

Sample Input 2

2
ab

Sample Output 2

ab

• When x=(), the s after the procedure is ab, the lexicographically smallest possible result.
• Note that x may have a length of 0.

Sample Input 3

16
cabaaabbbabcbaba

Sample Output 3

aaaaaaabbbbcbbbc

Sample Input 4

17
snwfpfwipeusiwkzo

Sample Output 4

effwpnwipsusiwkzo

见题面 Input 部分

见题面 Output 部分