CF1400A.String Similarity

A binary string is a string where each character is either 0 or 1. Two binary strings $a$ and $b$ of equal length are similar, if they have the same character in some position (there exists an integer $i$ such that $a_i = b_i$ ). For example:

• 10010 and 01111 are similar (they have the same character in position $4$ );
• 10010 and 11111 are similar;
• 111 and 111 are similar;
• 0110 and 1001 are not similar.

You are given an integer $n$ and a binary string $s$ consisting of $2n-1$ characters. Let's denote $s[l..r]$ as the contiguous substring of $s$ starting with $l$ -th character and ending with $r$ -th character (in other words, $s[l..r] = s_l s_{l + 1} s_{l + 2} \dots s_r$ ).

You have to construct a binary string $w$ of length $n$ which is similar to all of the following strings: $s[1..n]$ , $s[2..n+1]$ , $s[3..n+2]$ , ..., $s[n..2n-1]$ .

The first line contains a single integer $t$ ( $1 \le t \le 1000$ ) — the number of test cases.

The first line of each test case contains a single integer $n$ ( $1 \le n \le 50$ ).

The second line of each test case contains the binary string $s$ of length $2n - 1$ . Each character $s_i$ is either 0 or 1.

For each test case, print the corresponding binary string $w$ of length $n$ . If there are multiple such strings — print any of them. It can be shown that at least one string $w$ meeting the constraints always exists.

The explanation of the sample case (equal characters in equal positions are bold):

The first test case:

• $\mathbf{1}$ is similar to $s[1..1] = \mathbf{1}$ .

The second test case:

• $\mathbf{000}$ is similar to $s[1..3] = \mathbf{000}$ ;
• $\mathbf{000}$ is similar to $s[2..4] = \mathbf{000}$ ;
• $\mathbf{000}$ is similar to $s[3..5] = \mathbf{000}$ .

The third test case:

• $\mathbf{1}0\mathbf{10}$ is similar to $s[1..4] = \mathbf{1}1\mathbf{10}$ ;
• $\mathbf{1}01\mathbf{0}$ is similar to $s[2..5] = \mathbf{1}10\mathbf{0}$ ;
• $\mathbf{10}1\mathbf{0}$ is similar to $s[3..6] = \mathbf{10}0\mathbf{0}$ ;
• $1\mathbf{0}1\mathbf{0}$ is similar to $s[4..7] = 0\mathbf{0}0\mathbf{0}$ .

The fourth test case:

• $0\mathbf{0}$ is similar to $s[1..2] = 1\mathbf{0}$ ;
• $\mathbf{0}0$ is similar to $s[2..3] = \mathbf{0}1$ .