stack<string>  state;
    int q , t, del, pr;
    int i = 0;
    string s, res;  
    cin>>q;
    while(i < q)
    {   
        cin>>t;   
        if(t ==1)
        {
            //Append 
            cin>>s;
            state.push(res);
            res +=s;
            
        }else if(t ==2)
        {
            //Delete
            cin >> del;
            int index = res.length() - del;
            if(index < res.length())
            {
                state.push(res);
                res = res.erase(index,res.length());
            }
            
        }else if(t ==3)
        {
            //Print
            cin>>pr;
            int index = pr -1;
            if(index < res.length())
            {
                cout<<res[index] << endl;
            }
            
        }else if(t ==4)
        {
            //Undo
            if(!state.empty())
            {           
                string tp = state.top();
                res = tp;
                state.pop();
            }     
        }
        i++;
    }

    return 0;