class Editor:
    def __init__(self):
        """Initialize the text editor."""
        self.text = ""
        self.history = []

    def append(self, word):
        """Append a word to the end of the text."""
        self.history.append(self.text)
        self.text += word

    def delete(self, k):
        """Delete the last k characters from the text."""
        if 0 <= k <= len(self.text):
            self.history.append(self.text)
            self.text = self.text[:-k]
        else:
            raise ValueError("Cannot delete more characters than the length of the text.")

    def print_char(self, k):
        """Print the character at the specified index in the text."""
        if 1 <= k <= len(self.text):
            print(self.text[k - 1])
        else:
            raise IndexError("Index out of range.")

    def undo(self):
        """Undo the last operation by restoring the previous state of the text."""
        if self.history:
            self.text = self.history.pop()
        else:
            print("Nothing to undo.")

# Test the Editor class
editor = Editor()
count = int(input())
for _ in range(count):
    operation = input().split()
    op_code = operation[0]
    try:
        if op_code == '1':
            editor.append(operation[1])
        elif op_code == '2':
            editor.delete(int(operation[1]))
        elif op_code == '3':
            editor.print_char(int(operation[1]))
        elif op_code == '4':
            editor.undo()
        else:
            print("Invalid operation code.")
    except (ValueError, IndexError) as e:
        print(f"Error: {e}")