Joe recently flunked the CCC (Canadian Computing Competition) and has decided to switch from programming to colouring instead.

In order for a chance to qualify for the prestigious Canadian Colouring Olympiad (CCO), he needs to be able to be able to colour a "good" stripe pattern, which consists of a row of colours that alternate between colour ~0~ and colour ~1~. Examples of good stripe patterns include ~010101~ and ~101~ but not ~100~.

After realizing that he just painted a bad stripe pattern, Joe plans to use his magic paintbrush, which, in a single stroke can change the colour of a single position on his pattern from either colour ~0~ to colour ~1~ or vice versa. Given Joe's current stripe pattern as a string of ~0~s and ~1~s, determine the minimum number of magic brush strokes Joe needs to make his stripe pattern "good".

Input Specification

The first line contains an integer ~N~ ~(1 \le N \le 2 \times 10^5)~, the length of his pattern.

The second line contains a string of ~N~ characters, each consisting of either ~0~ or ~1~.

Subtask 1 [5%]

The original pattern will only consist of colour ~0~.

Subtask 2 [10%]

~1 \le N \le 18~

Subtask 3 [85%]

No additional constraints

Output Specification

Output one integer: the minimum number of magic brush strokes needed to turn is pattern into a "good" stripe pattern.

Sample Input

5
01011

Sample Output

1

Explanation for Sample Case

Joe can use his magic paintbrush to turn the last stripe to colour ~0~, making the pattern ~01010~, which is a "good" stripe pattern, taking a total of 1 magic brush stroke.