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
stones = gets.chomp.split("")

# 黒か白の片方しかない場合
if stones.uniq.size == 1
  puts 0
else
  count = []
  # 左から白を探していくパターン
  black_flag = false
  stones.each_with_index do |stone, i|
    if stone == "#"
      black_flag = true
    elsif black_flag && stone == "."
      count << stones[i..-1].count(".")
      break
    end
  end
  # 右から黒を探していくパターン
  stones.reverse!
  white_flag = false
  stones.each_with_index do |stone, i|
    if stone == "."
      white_flag = true
    elsif white_flag && stone == "#"
      count << stones[i..-1].count("#")
      break
    end
  end
  puts count.min
end