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)

N = gets.to_i
S = gets.chomp

prev = S[0]
count = 0
strings = []
S.chars.each do |s|
  if prev == s
    count += 1
  else
    strings << [prev, count]
    count = 1
  end
  prev = s
end
strings << [prev, count]

# p strings

ans = 0
prev = strings.first
strings[1..-1].each do |array|
  s = array[0]
  cnt = array[1]
  if s == '.' && prev[0] == '#'
    if prev[1] > cnt
      array[0] = prev[0]
      ans += cnt
    else
      prev[0] = array[0]
      ans += prev[1]
    end
  end
  prev = array
end

p ans