CF746B.Decoding

Polycarp is mad about coding, that is why he writes Sveta encoded messages. He calls the median letter in a word the letter which is in the middle of the word. If the word's length is even, the median letter is the left of the two middle letters. In the following examples, the median letter is highlighted: contest, info. If the word consists of single letter, then according to above definition this letter is the median letter.

Polycarp encodes each word in the following way: he writes down the median letter of the word, then deletes it and repeats the process until there are no letters left. For example, he encodes the word volga as logva.

You are given an encoding s of some word, your task is to decode it.

波利卡普痴迷于编程，因此他会给斯维塔发送加密消息。他将一个单词中的“中位字母”定义为位于该单词正中间的字母。如果单词长度为偶数，则中位字母取中间两个字母中靠左的那个。在以下示例中，中位字母已被高亮显示：contest、info。若单词仅含一个字母，则根据上述定义，该字母即为中位字母。

波利卡普按如下方式对每个单词进行编码：他先写出该单词的中位字母，然后将其删除，并重复此过程，直至单词中无剩余字母。例如，他对单词 volga 的编码结果为 logva。

现给你一个某单词的编码结果 $ s $，你的任务是将其解码。

The first line contains a positive integer n (1 ≤ n ≤ 2000) — the length of the encoded word.

The second line contains the string s of length n consisting of lowercase English letters — the encoding.

第一行包含一个正整数 $n$（$1 \leq n \leq 2000$）—— 编码单词的长度。

第二行包含一个长度为 $n$ 的字符串 $s$，由小写英文字母组成——该编码。

Print the word that Polycarp encoded.

输出 Polycarp 编码的单词。

In the first example Polycarp encoded the word volga. At first, he wrote down the letter l from the position 3, after that his word looked like voga. After that Polycarp wrote down the letter o from the position 2, his word became vga. Then Polycarp wrote down the letter g which was at the second position, the word became va. Then he wrote down the letter v, then the letter a. Thus, the encoding looked like logva.

In the second example Polycarp encoded the word no. He wrote down the letter n, the word became o, and he wrote down the letter o. Thus, in this example, the word and its encoding are the same.

In the third example Polycarp encoded the word baba. At first, he wrote down the letter a, which was at the position 2, after that the word looked like bba. Then he wrote down the letter b, which was at the position 2, his word looked like ba. After that he wrote down the letter b, which was at the position 1, the word looked like a, and he wrote down that letter a. Thus, the encoding is abba.

在第一个例子中，Polycarp 对单词 volga 进行了编码。他首先写下位于位置 3 的字母 l，此时单词变为 voga；接着他写下位于位置 2 的字母 o，单词变为 vga；然后他写下位于位置 2 的字母 g，单词变为 va；之后他写下字母 v，再写下字母 a。因此，该编码结果为 logva。

在第二个例子中，Polycarp 对单词 no 进行了编码。他先写下字母 n，此时单词变为 o，然后他写下字母 o。因此，在本例中，原单词与其编码完全相同。

在第三个例子中，Polycarp 对单词 baba 进行了编码。他首先写下位于位置 2 的字母 a，此时单词变为 bba；接着他写下位于位置 2 的字母 b，单词变为 ba；然后他写下位于位置 1 的字母 b，单词变为 a；最后他写下该字母 a。因此，该编码结果为 abba。