CF327A Flipping Game

Iahub got bored, so he invented a game to be played on paper. He writes $ n $ integers $ a_{1},a_{2},...,a_{n} $ . Each of those integers can be either 0 or 1. He's allowed to do exactly one move: he chooses two indices $ i $ and $ j $ ( $ 1

The first line of the input contains an integer $ n $ ( $ 1

Print an integer — the maximal number of 1s that can be obtained after exactly one move.

In the first case, flip the segment from 2 to 5 $ (i=2,j=5) $ . That flip changes the sequence, it becomes: \[1 1 1 0 1\]. So, it contains four ones. There is no way to make the whole sequence equal to \[1 1 1 1 1\]. In the second case, flipping only the second and the third element $ (i=2,j=3) $ will turn all numbers into 1.