#62 01 10

Statement

Statement language

A string $S$ of length $N$ consisting of $0$ s and $1$ s is given. By repeatedly performing the operation of swapping two adjacent characters, you want to make the number of adjacent character pairs that are different from each other be even. Find the minimum number of operations required. Print -1 if it is impossible.

Input

The input is given in the following format.

$N$ $S$

Output

Print the answer to the problem on the first line.

Constraints

$2 \le N \le 200 \ 000$ .
$S_i \in \{0, 1\}$ ().

Subtasks

#	Score	Constraints
1	22	There is exactly one $1 \leq i \leq N$ such that $S_i = 1$ .

Samples

Sample 1

Input

3
011

Output

1

Sample 2

Input

2
01

Output

-1