Given a string S consisting only of opening and closing parenthesis 'ie '('  and ')', find out the length of the longest valid(well-formed) parentheses substring.
NOTE: Length of smallest the valid substring ( ) is 2.

Example 1:

Input: S = "(()("
Output: 2
Explanation: The longest valid 
substring is "()". Length = 2.

Example 2:

Input: S = "()(())("
Output: 6
Explanation: The longest valid 
substring is "()(())". Length = 6.

Your Task:  
You dont need to read input or print anything. Complete the function findMaxLen() which takes S as input parameter and returns the maxlength.

Expected Time Complexity:O(n)
Expected Auxiliary Space: O(1)   

Constraints:
1 <= |S| <= 10⁵