class Solution {
public:
    int evalRPN(vector<string>& tokens) {
        stack<int> stk;

        for (auto &s : tokens)
        {
            if (s == "+" || s == "-" || s == "*" || s == "/")
            {
                int b = stk.top(); stk.pop();
                int a = stk.top(); stk.pop();
                if (s == "+")   a += b;
                else if (s == "-")  a -= b;
                else if (s == "*")  a *= b;
                else    a /= b;
                stk.push(a);
            }
            else    stk.push(stoi(s));
        }

        return stk.top();
    }
};