## Description

Letters and antiletters can sometimes annihilate each other if they are too close. For example, the antiletter
a- would annilate the letter a, which we write as a+ to avoid confusion. In fact, a- does not annihilate
any other letters. Similarly, b- annihilates only b+ and so on. A letter and a corresponding antiletter will
annihilate each other if they are next to each other.

Given a string of letters and antiletters, we would like to know what is left after all anihilations occur.

## Input

Each line will consist of a string of letters and antiletters of length at most 5 * 10^{5}. Each letter or antiletter
is a lower case characters followed by a symbol + or -. The input terminates with an empty line. There will
be at most 30 lines in total.

## Output

For each line, output the string after all anihilations have occured.

## Sample Input

a+a-b+
a+b+c+c-b-a-
a+

## Sample Output

b+
a+

## Source

Northeast North-America 2009,
practice contest