#include <iostream>

#include <string>

#include <vector>

#include<stack>

using namespace std;

class Solution {

public:

    int toNum(string str)

    {

        int sum = ;

        int i = ;

        int flagPositiveOrNegative = ;;

        if(str[] == '-')

        {

            flagPositiveOrNegative = -;

            i = ;

        }

        for( i;i<str.size();i++)

        {

            sum *= ;

            sum += str[i] - '';

        }

        return sum * flagPositiveOrNegative;

    }

    int evalRPN(vector<string> &tokens) {

        if(tokens.size()==)

            return ;

        int i = ;

        stack<int> myStack;

        while(i<tokens.size())

        {

            if(tokens[i] == "+" || tokens[i] == "-" || tokens[i]=="*" ||tokens[i] == "/" )

            {

                int num1 = myStack.top();

                myStack.pop();

                int num2 = myStack.top();

                myStack.pop();

                if(tokens[i] == "+")

                    myStack.push(num1+num2);

                if(tokens[i] == "-")

                    myStack.push(num2-num1);

                if(tokens[i] == "*")

                    myStack.push(num1*num2);

                if(tokens[i] == "/")

                    myStack.push(num2/num1);

            }

            else

            {

                myStack.push(toNum(tokens[i]));

            }

            i++;

        }

        return myStack.top();

    }

};

int main()

{

    Solution myS;

    vector<string> input;

    input.push_back("");

    input.push_back("-4");

    input.push_back("+");

    cout<<myS.evalRPN(input);

    return ;

}