A. String Similaritytime limit per test2 secondsmemory limit per test256 megabytesinputstandard inputoutputstandard outputA 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].InputThe 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.OutputFor 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.ExampleInput
4
1
1
3
00000
4
1110000
2
101
Output
1
000
1010
00
NoteThe 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. 
4
1
1
3
00000
4
1110000
2
101

1 000 1010 00 
['constructive algorithms', 'strings', '*800']