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 $S \\gt T$.

1. 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.
2. 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.
3. 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.

Constraints

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

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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.

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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.

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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 $0$.

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Sample Input 3

16
cabaaabbbabcbaba

Sample Output 3

aaaaaaabbbbcbbbc

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Sample Input 4

17
snwfpfwipeusiwkzo

Sample Output 4

effwpnwipsusiwkzo