PROGRAMMING:Longest valid bracket string

Given a bracket string exp with only left and right brackets, find out the longest valid bracket string.
###Input format:
Enter a bracket string with only left and right parentheses to end with a new line.
###Output format:
Output the longest valid bracket string. The output has a space after each bracket.
###Input example:
```in
())(()())
```
###Output example:
The corresponding output is given here. For example:
```out
( ( ) ( ) )
```







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