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Right-Left Cipher

题面翻译

题目描述

Polycarp喜欢密码。 他发明了自己的密码，称为“右-左”（？应该是这个意思吧？）。

“右-左”密码用于加密字符串。

Polycarp使用以下算法加密字符串，$S = S_1S_2S_3 ... S_n$:

他写下$S_1$，他用$S_2$接上当前的单词（即将$S_2$写到当前结果的右边），

他在$S_3$前面加上当前的单词（即在当前结果的左边写下$S_3$），

他将$S_4$接上当前单词（即将$S_4$写到当前结果的右侧），

他在$S_5$前面加上当前的单词（即在当前结果的左边写下$S_5$）...

这么做直到处理完$S$。

举个例子，如果$S =$"techno"，那么处理过程就是： "t" → "te" → "cte" → "cteh" → "ncteh" → "ncteho"。所以加密"techno"后的字符串就是"ncteho"。

现在给你一个字符串$t$，即加密后的字符串，你的任务就是找到原来的字符串$S$

输入输出格式

输入格式：

只有一行，$t$，加密后的字符串，只包含小写字母，$1<= t_{len} <=50$

输出格式：

一行，原字符串$S$。

题目描述

Polycarp loves ciphers. He has invented his own cipher called Right-Left.

Right-Left cipher is used for strings. To encrypt the string $s=s_{1}s_{2} \dots s_{n}$ Polycarp uses the following algorithm:

• he writes down $s_1$ ,
• he appends the current word with $s_2$ (i.e. writes down $s_2$ to the right of the current result),
• he prepends the current word with $s_3$ (i.e. writes down $s_3$ to the left of the current result),
• he appends the current word with $s_4$ (i.e. writes down $s_4$ to the right of the current result),
• he prepends the current word with $s_5$ (i.e. writes down $s_5$ to the left of the current result),
• and so on for each position until the end of $s$ .

For example, if $s$ ="techno" the process is: "t" $\to$ "te" $\to$ "cte" $\to$ "cteh" $\to$ "ncteh" $\to$ "ncteho". So the encrypted $s$ ="techno" is "ncteho".

Given string $t$ — the result of encryption of some string $s$ . Your task is to decrypt it, i.e. find the string $s$ .

输入格式

The only line of the input contains $t$ — the result of encryption of some string $s$ . It contains only lowercase Latin letters. The length of $t$ is between $1$ and $50$ , inclusive.

输出格式

Print such string $s$ that after encryption it equals $t$ .

样例 #1

样例输入 #1

ncteho

样例输出 #1

techno

样例 #2

样例输入 #2

erfdcoeocs

样例输出 #2

codeforces

样例 #3

样例输入 #3

z

样例输出 #3

z