int evalRPN(vector<string>& tokens) {
        int n=tokens.size();
        stack<int> s1;
        for(int i=0;i<n;i++){
            if(tokens[i]=="+"||tokens[i]=="-"||tokens[i]=="*"||tokens[i]=="/"){
                unsigned int t1=s1.top();
                s1.pop();
                unsigned int t2=s1.top();
                s1.pop();
                unsigned int t3=0;
                if(tokens[i]=="+")
                t3=t1+t2;
                else if(tokens[i]=="-")
                t3=t2-t1;
                else if(tokens[i]=="*")
                t3=t1*t2;
                else t3=t2/t1;

                s1.push(t3);
            }
            else{
                int temp=stoi(tokens[i]);
                s1.push(temp);
            }
        }
        int ans=s1.top();
        return ans;
    }