class Solution {
public:
    string largestOddNumber(string num) {
        // Traverse the string from the end
        for (int i = num.size() - 1; i >= 0; --i) {
            // If the current character is an odd digit
            if ((num[i] - '0') % 2 != 0) {
                // Return the substring from the start to the current position
                return num.substr(0, i + 1);
            }
        }
        // If no odd digit is found, return an empty string
        return "";
    }
};

class Solution {
public:
    string removeOuterParentheses(string s) {
        string result;
        stack<char> stack;
        int start = 0;  // Start index of a primitive block
        int n = s.size();
        for(int i = 0; i <n; i++){
            if(s[i] == '(') {
                stack.push('(');
            }else{
                stack.pop();
            }
            // When the stack is empty, we found a complete primitive block
            if(stack.empty()){
                // Append all except the outermost parentheses
                result += s.substr(start + 1, i - start - 1);
                start = i + 1;  // Update the start for the next primitive block
            }
        }

        return result;
    }
};