import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

/**
 * Created by zz on 2023/11/5
 */
public class Memo {
    private static List<Integer> offsets = new ArrayList<>();
    private final static String fileName = "/Users/szhang/Project75/src/text.txt";

    public static void main(String[] args) throws IOException {
        String contents = new BufferedReader(new FileReader(fileName)).readLine();
        while (true) {
            try {
                // keep scanning input from user;
                String reader = new Scanner(System.in).nextLine();
                // if input is (:list), then print out file content;
                if (":list".equals(reader)) {
                    System.out.println(contents);
                } else if (":undo".equals(reader)) {
                    int offset = offsets.get(offsets.size() - 1);
                    offsets.remove(offsets.size() - 1);
                    contents = contents.substring(0, contents.length() - offset);
                    BufferedWriter writer = new BufferedWriter(new FileWriter(fileName));
                    writer.write(contents);
                } else {
                    String newContent = reader;
                    offsets.add(newContent.length());
                    contents += newContent;
                    BufferedWriter writer = new BufferedWriter(new FileWriter(fileName));
                    writer.write(contents);
                }
            } catch (Exception ignored) {

            }
            // if input is (:undo), then remove last time input and print out file the latest content;
            // use an offset to keep tracking previous added string length;
        }
    }
}

public class InputText {
  private StringBuilder text = new StringBuilder();

  public String getText() {
    return text.toString();
  }

  public void append(String input) {
    text.append(input);
  }

  public void setText(String text) {
    this.text.replace(0, this.text.length(), text);
  }
}

public class SnapshotHolder {
  private Stack<InputText> snapshots = new Stack<>();

  public InputText popSnapshot() {
    return snapshots.pop();
  }

  public void pushSnapshot(InputText inputText) {
    InputText deepClonedInputText = new InputText();
    deepClonedInputText.setText(inputText.getText());
    snapshots.push(deepClonedInputText);
  }
}

public class ApplicationMain {
  public static void main(String[] args) {
    InputText inputText = new InputText();
    SnapshotHolder snapshotsHolder = new SnapshotHolder();
    Scanner scanner = new Scanner(System.in);
    while (scanner.hasNext()) {
      String input = scanner.next();
      if (input.equals(":list")) {
        System.out.println(inputText.getText());
      } else if (input.equals(":undo")) {
        InputText snapshot = snapshotsHolder.popSnapshot();
        inputText.setText(snapshot.getText());
      } else {
        snapshotsHolder.pushSnapshot(inputText);
        inputText.append(input);
      }
    }
  }
}

public class InputText {
  private StringBuilder text = new StringBuilder();

  public String getText() {
    return text.toString();
  }

  public void append(String input) {
    text.append(input);
  }

  public Snapshot createSnapshot() {
    return new Snapshot(text.toString());
  }

  public void restoreSnapshot(Snapshot snapshot) {
    this.text.replace(0, this.text.length(), snapshot.getText());
  }
}

public class Snapshot {
  private String text;

  public Snapshot(String text) {
    this.text = text;
  }

  public String getText() {
    return this.text;
  }
}

public class SnapshotHolder {
  private Stack<Snapshot> snapshots = new Stack<>();

  public Snapshot popSnapshot() {
    return snapshots.pop();
  }

  public void pushSnapshot(Snapshot snapshot) {
    snapshots.push(snapshot);
  }
}

public class ApplicationMain {
  public static void main(String[] args) {
    InputText inputText = new InputText();
    SnapshotHolder snapshotsHolder = new SnapshotHolder();
    Scanner scanner = new Scanner(System.in);
    while (scanner.hasNext()) {
      String input = scanner.next();
      if (input.equals(":list")) {
        System.out.println(inputText.toString());
      } else if (input.equals(":undo")) {
        Snapshot snapshot = snapshotsHolder.popSnapshot();
        inputText.restoreSnapshot(snapshot);
      } else {
        snapshotsHolder.pushSnapshot(inputText.createSnapshot());
        inputText.append(input);
      }
    }
  }
}