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 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 $$$s[2..3] = \mathbf{0}1$$$. 
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.
for s in [*open(0)][2::2]:
    print(s[::2])
for s in [*open(0)][2::2]:
    print(s[::2])
for s in [*open(0)][2::2]:
    print(s[::2])