Write down the numbers in a row and separate them with minus signs .
We want to add pairs of parentheses to form a valid expression such that each pair of parentheses contains exactly one minus sign, not counting those contained in its subparentheses.
For example, when , we can form five different expressions in this way:
The sum of the values of these expressions is equal to .
Let be the sum of the values of all different expressions that can be obtained in this way.
Thus . Moreover, and .
Find .
Write-up coming later
The complete problem is available here. An approach, code, and answer will be added later.