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)

#gets.to_i
#data = gets.split(" ").map{|nn|nn.to_i}
#n = data[]
#m = data[]
#a = data[]
#a = data[]
#c = data[]
#n.times do
#end

data = gets.chomp.chars

cost_first_white = 0
for i in 0..(data.size-1) do
  if i % 2 == 0
    if data[i] == "0"
    else
      cost_first_white += 1
    end
  else
    if data[i] == "1"
    else
      cost_first_white += 1
    end
  end

end
cost_first_black = 0

for i in 0..(data.size-1) do
  if i % 2 == 0
    if data[i] == "1"
      next
    else
      cost_first_black += 1
    end
  else
    if data[i] == "0"
      next
    else
      cost_first_black += 1
    end
  end
end


if cost_first_black < cost_first_white
  puts cost_first_black.to_s
else
  puts cost_first_white.to_s
end