simpletexteditor

#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
#include <bits/stdc++.h>

using namespace std;


int main() {
    int t_case,i=0,ip,k;
    string w;
    string s;
    s="";

    stack <string> undo;

    cin>>t_case;
    while(i<t_case){
        cin>>ip;
        switch(ip){
            case 1:
                undo.push(s);
                cin>>w;
                s=s+w;
                break;
            case 2:
                cin>>k;
                undo.push(s);
                s.erase(s.end()-k,s.end());
                break;
            case 3:
                cin>>k;
                cout<<s.at(k)<<endl;
            case 4:
                s=undo.top();
                undo.pop();
                break;

        }
        i++;
    }
    return 0;
}