<? echo $row['title']." - ".$MSG_PROBLEM."

A list is a sequence of or more elements, expressed in this form: [a 1 , a 2 , a 3 , ... , a n ], where each a i

is or more consecutive digits or lowercase letters. i.e. each list begins with a left square bracket,

then zero or more elements separated by a single comma, followed by a right square bracket. There will

be no whitespace characters (spaces, TABs etc) within a list.

In this problem, we use two list operations: append (++) and remove (--).

1. A ++ B: append elements in B to the end of A.

2. A -- B: remove all the elements in B, from A. If something appears more than once in B, remove it that

many times in A. If there are many equal elements in A to choose from, remove them from left to right

(until all occurrences are removed, or there is no need to remove more elements).

Your task is to write a calculator, evaluating simple expressions or the form "list1 ++ list2" or "list1 --

list2".

There will be at most 10 expressions, one in each line, each having the form "list1 ++ list2" or "list1 --

list2", with no more than 80 characters in total (not counting the newline character). There will be exactly

two spaces in each line: one before and one after the operator. Input ends with a single dot. The input is

guaranteed to satisfy the restrictions stated above.

For each expression, print its result on a single line.

[1,2,3] ++ [1,2,3]
[a,b,c,t,d,e,t,x,y,t] -- [t]
[a,b,c,t,d,e,t,x,y,t] -- [t,t,t,t]
[123] ++ [456]
.

[1,2,3,1,2,3]
[a,b,c,d,e,t,x,y,t]
[a,b,c,d,e,x,y]
[123,456]