Simple Text Editor with Undo

You are given a text editor that starts with an empty string. You will be provided a number of operations to perform on the string. Each operation is either adding a character to the end of the string or undoing the most recent add operation. Formally, the operations can be described as follows:

For each operation:

• If the operation is of the form ADD x (where x is a single character), append x to the end of the current string.
• If the operation is UNDO, remove the last added character from the current string if there is any.

Mathematically, if we denote the string after performing i operations as \( S_i \), then for an operation ADD x, we have \( S_i = S_{i-1} + x \); for UNDO, if \( S_{i-1} \) is non-empty, then \( S_i \) is \( S_{i-1} \) with its last character removed.

Your task is to compute the final state of the string after all operations have been executed.

inputFormat

The input is given via stdin:

• The first line contains a single integer n (1 ≤ n ≤ 10^5), representing the number of operations.
• The following n lines each contain an operation, either in the form ADD x where x is a single character, or UNDO.

outputFormat

Output the final string after performing all the operations. The output should be written to stdout as a single line.

## sample

5
ADD a
ADD b
UNDO
ADD c
ADD d

acd

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