Text Editor Undo/Redo Simulator

A simplified text editor holds a single line of text, starting empty. It supports m operations, each one of:

• TYPE s — append the token s (non-empty, lowercase letters and digits only, no spaces) to the end of the current text.
• DELETE k — remove the last k characters of the current text (it is guaranteed that k does not exceed the current text's length).
• UNDO — revert the text to the state it was in immediately before the most recent TYPE/DELETE operation that has not already been undone. If there is nothing left to undo, this operation does nothing.
• REDO — reapply the most recently undone operation. If there is nothing to redo (either nothing has been undone, or a new TYPE/DELETE was performed since the last undo, which discards the redo history), this operation does nothing.

Process all m operations in order and report the final text.

Input format

Line 1: an integer m. Next m lines: one operation each, in the form described above.

Output format

A single line: the final text (an empty line if the final text is empty).

Constraints

• 1 ≤ m ≤ 1000
• For TYPE s: 1 ≤ length of s ≤ 20, lowercase English letters and digits only.
• For DELETE k: 1 ≤ k ≤ current text length.
• The final text length never exceeds 20000 characters.