Given a number N and string S of digits denoting a positive integer [ N < sizeof(S) ] , build the lowest number possible by removing N digits from S, without changing their order.
The first line of input contains an integer T denoting the number of test cases. Then T test cases
The first line of each test case contains a positive integer N.
The second line of each test case contains a string of digits denoting a positive integer S.
NOTE: N should be less than length of (S).
Print out the smallest number possible.
1 <= T <= 100
0 < S <= 30
0 < N <= 10
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