50th Mathematical Olympiad in Ukraine, Third Round (January 23, 2010)

In the expression $$12-11-10-9-8-7-6-5-4-3-2-1$$ there are somehow placed brackets and the value is calculated. Find the maximum value that can be reached. Justify your answer.

Notice. Left bracket can be placed only before a number and right - only after. For example, expressions $-4(-3-2)$ and $-(4-3-2)$ are incorrect.