This is yet another problem dealing with regular bracket sequences.

We should remind you that a bracket sequence is called regular, if by inserting «+» and «1» into it we can get a correct mathematical expression. For example, sequences «(())()», «()» and «(()(()))» are regular, while «)(», «(()» and «(()))(» are not. 

You are given a string of «(» and «)» characters. You are to find its longest substring that is a regular bracket sequence. You are to find the number of such substrings as well.
The first line of the input file contains a non-empty string, consisting of «(» and «)» characters. Its length does not exceed 10<sup class="upper-index">6</sup>.
def main():
    s = raw_input()
    ans = 0
    stk = []

    for right, x in enumerate(s):
        if x == "(":
            stk.append(right)
        else:
            if stk and s[stk[-1]] == "(":
                idx = stk.pop()
                if stk:
                    ans = max(ans, right - stk[-1])
                else:
                    ans = max(ans, right+1)
            else:
                stk.append(right)
        
    
    return ans