For Java 7. Ok. You need to know that i generated this by chatGPT, tell him to optimize my oringinal. Eventhrough it's still not good enough, but try a few times then it might pass.

import java.util.Scanner; import java.util.Stack;

public class SolutionSolution { public static void main(String[] args) { Scanner scanner = new Scanner(System.in); int q = scanner.nextInt(); scanner.nextLine();

    StringBuilder currentText = new StringBuilder();
    Stack<Operation> history = new Stack<>();

    for (int i = 0; i < q; i++) {
        int type = scanner.nextInt();

        switch (type) {
            case 1: // Append
                String w = scanner.next();
                history.push(new Operation(1, w.length()));
                currentText.append(w);
                break;

            case 2: // Delete
                int k = scanner.nextInt();
                String deletedText = currentText.substring(currentText.length() - k);
                history.push(new Operation(2, deletedText));
                currentText.delete(currentText.length() - k, currentText.length());
                break;

            case 3: // Print
                int pos = scanner.nextInt();
                System.out.println(currentText.charAt(pos - 1));
                break;

            case 4: // Undo
                if (!history.isEmpty()) {
                    Operation lastOperation = history.pop();
                    if (lastOperation.type == 1) {
                        // Undo append: remove the last 'length' characters
                        currentText.delete(currentText.length() - lastOperation.length, currentText.length());
                    } else if (lastOperation.type == 2) {
                        // Undo delete: append the deleted string
                        currentText.append(lastOperation.data);
                    }
                }
                break;

            default:
                break;
        }
    }

    scanner.close();
}

static class Operation { int type; // 1 for append, 2 for delete int length; String data;

    Operation(int type, int length) {
        this.type = type;
        this.length = length;
    }

    Operation(int type, String data) {
        this.type = type;
        this.data = data;
    }
}

}