403075: GYM100989 M Plus or Minus (B)

George met AbdelKader in the corridor of the CS department busy trying to fix a group of incorrect equations. Seeing how fast he is, George decided to challenge AbdelKader with a very large incorrect equation. AbdelKader happily accepted the challenge!

The first line of input contains an integer N (2 ≤ N ≤ 300), the number of terms in the equation.

The second line contains N integers separated by a plus + or a minus -, each value is between 1 and 300.

Values and operators are separated by a single space.

If it is impossible to make the equation correct by replacing operators, print  - 1, otherwise print the minimum number of needed changes.

7
1 + 1 - 4 - 4 - 4 - 2 - 2

3

3
5 + 3 - 7

-1