PROGRAMMING:String input exercise (IV)
The substring of the output string.
###Input format:
The first line is a positive integer n, and then there are N sets of tests.
Each set of tests starts with a positive integer k, followed by a string s, separated by spaces between K and s（ Length of K greater than 0 and less than or equal to s)
###Output format:
For each group of tests, output a substring of length k from the beginning.
###Input example:
```in
two
2 hello world!
10 welcome to acm world
```
###Output example:
```out
he
welcome to
```
answer：If there is no answer, please comment
###Input format:
The first line is a positive integer n, and then there are N sets of tests.
Each set of tests starts with a positive integer k, followed by a string s, separated by spaces between K and s（ Length of K greater than 0 and less than or equal to s)
###Output format:
For each group of tests, output a substring of length k from the beginning.
###Input example:
```in
two
2 hello world!
10 welcome to acm world
```
###Output example:
```out
he
welcome to
```
answer：If there is no answer, please comment