class Solution {
    int evaluate(std::string& s) {
        int ans=0;
        bool plus=true;
        int ii=0;
        std::string::size_type sz;
        while(ii<s.length()) {
            if (s[ii]=='(' || s[ii]==')') {
                ++ii;
                continue;
            }
            if (s[ii]==' '){
                ++ii;
                continue;
            }
            if (s[ii]=='+'){
                if (s[ii+1]=='-') {
                    plus=false;
                    ii+=2;
                }
                else {
                plus=true;
                ++ii;
                }
                continue;
            }
            else if (s[ii]=='-') {
                if (s[ii+1]=='-') {
                    plus=true;
                    ii+=2;
                }
                else{
                plus=false;
                ++ii;
                }
                continue;
            }
            else {
                // we have digits here.. get the number..
                std::string num="";
                //std::cout<<int(s[ii])<<std::endl;
                while(s[ii]>=48 && s[ii]<=57) {
                //std::cout<<s[ii]<<std::endl;
                    num+=s[ii];
                    ++ii;
                }
                //digit constructed..
                int digi = std::stoi (num,&sz);
                if (plus)
                    ans += digi;
                else
                    ans -= digi;
            }
        }
        return ans;
    }
public:
    int calculate(string s) {
        if (s.empty())
            return 0;
        std::stack<string> stk;
        for (int ii=0; ii<s.length(); ++ii) {
            if (s[ii]==')'){
                // Pop till '(' and create string and send and then push..
                std::string exp = "";
                while (!stk.empty() && stk.top()!="("){
                    exp = stk.top()+exp;
                    stk.pop();
                }
                stk.pop();
                stk.push(std::to_string(evaluate(exp)));
            }
            else {
                stk.push(std::string(1,s[ii]));
            }
        }

        std::string exp = "";
        while (!stk.empty() && stk.top()!="("){
            exp = stk.top()+exp;
            stk.pop();
        }

        return evaluate(exp);


    }
};