Problem:
Score : 300 points

Problem Statement

There are N stones arranged in a row. Every stone is painted white or black.
A string S represents the color of the stones. The i-th stone from the left is white if the i-th character of S is ., and the stone is black if the character is #.

Takahashi wants to change the colors of some stones to black or white so that there will be no white stone immediately to the right of a black stone.
Find the minimum number of stones that needs to be recolored.

Constraints

1 \leq N \leq 2\times 10^5

S is a string of length N consisting of . and #.

Input

Input is given from Standard Input in the following format:

N
S

Output

Print the minimum number of stones that needs to be recolored.

Sample Input 1

3
#.#

Sample Output 1

1

It is enough to change the color of the first stone to white.

Sample Input 2

5
#.##.

Sample Output 2

2

Sample Input 3

9
.........

Sample Output 3

0

Solution in Ruby (2.3.3) (judge verdict: Wrong Answer)

length = gets.to_i
str = gets.strip.to_s
reverse = str.reverse

ex_ch = nil
count = 0

w_count = 0
b_count = 0

str.each_char do |ch|
  if ch == '.'
    w_count += 1
  else
    b_count += 1
  end
end

if b_count > w_count
  str.each_char do |ch|
    if ch == '.' && ex_ch =='#'
      count += 1
      ex_ch = '#'
    else
      ex_ch = ch
    end
  end
else
  reverse.each_char do |ch|
    if ch == '#' && ex_ch =='.'
      count += 1
      ex_ch = '.'
    else
      ex_ch = ch
    end
  end
end

puts count