1234 - 56 - 789 => 389

This is silly but I can't figure out what the solution should be for n = 389, apparently the answer is 2.

123 + 456 + 789 => 1368
123 + 456 - 789 => -210
123 - 456 + 789 => 456
123 - 456 - 789 => -1122

How do we get to 2?