Problem:
Score : 300 points

Problem Statement

N tiles are arranged in a row from left to right. The initial color of each tile is represented by a string S of length N.

The i-th tile from the left is painted black if the i-th character of S is 0, and painted white if that character is 1.

You want to repaint some of the tiles black or white, so that any two adjacent tiles have different colors.

At least how many tiles need to be repainted to satisfy the condition?

Constraints

1 \leq |S| \leq 10^5

S_i is 0 or 1.

Input

Input is given from Standard Input in the following format:

S

Output

Print the minimum number of tiles that need to be repainted to satisfy the condition.

Sample Input 1

000

Sample Output 1

1

The condition can be satisfied by repainting the middle tile white.

Sample Input 2

10010010

Sample Output 2

3

Sample Input 3

0

Sample Output 3

0

Solution in Ruby (2.3.3) (judge verdict: Accepted)

strs = gets.strip.split('')

_slice = strs.each_slice(2)
odd_strs = _slice.map(&:first)
even_strs = _slice.map(&:last)
even_strs.pop if strs.size % 2 == 1

odd_strs_one_count = odd_strs.count('1')
odd_strs_zero_count = odd_strs.size - odd_strs_one_count

even_strs_one_count = even_strs.count('1')
even_strs_zero_count = even_strs.size - even_strs_one_count

change_count_pattern1 = odd_strs_one_count + even_strs_zero_count
change_count_pattern2 = odd_strs_zero_count + even_strs_one_count

if change_count_pattern1 <= change_count_pattern2
  puts change_count_pattern1
else
  puts change_count_pattern2
end