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)

# frozen_string_literal: true

# 愚直にやればいい気がする
# ↑無能 .#..#...#..は7
# なので初めて#が出てきたら以降はもう駄目
# ↑無能 というか問題文読んでなかった
# 白しか反転できないかと思ってた
# なので .#..#...#.. は3
# 黒いのが少ないならそっちを変えたほうがいいっぽい
# あと必要ないのは 初出が連続する#でおわる感じのやつ

n = gets.chomp.to_i
s = gets.chomp.chars

# なぜか効かない
# if s.index('#.').nil?
#   puts s.index('#.')
#   exit
# end

ans = 0
black_count = 0
flag = false
whiteon = false
(1...n).to_a.each do |i|
  if i == n - 1 && s[i] == '#'
    next
  elsif i < n - 1 && s[i] == '#'
    flag = true
    black_count += 1
  end

  if flag && s[i] == '.'
    ans += 1
  elsif s[i - 1] == '#' && s[i] == '.'
    ans += 1
    flag = true
    whiteon = true
  end
end
if whiteon == false
  puts 0
else
  if [ans, black_count].min != 0
    puts [ans, black_count].min
  else
    puts [ans, black_count].max
  end
end