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.chars
left_start = -1
right_start = -1
left_ans = 10000000
right_ans = 10000000
s.each_with_index do|chara, index|
  if chara == "#" && left_start == -1
    left_start = index
    left_ans = 0
  end
  if left_start != -1
    if chara == "."
      left_ans += 1
    end
  end
end

if left_start != -1
  s = s.reverse
  s.each_with_index do|chara, index|
    if chara == "." && right_start == -1
      right_start = index
      right_ans = 0
    end
    if right_start != -1
      if chara == "#"
        right_ans += 1
      end
    end
  end
  right_ans = 0
  s.each do|chara|
    if chara == "#"
      right_ans += 1
    end
  end
  if right_ans == 0
    right_ans = 200000000
  end

  another_ans = 0
  s.each do|chara|
    if chara == "."
      another_ans += 1
    end
  end
  if another_ans == 0
    another_ans = 200000000
  end

  if right_start == -1
    puts "0"
  else
    puts [left_ans, right_ans, another_ans].min.to_s
  end
else
  puts "0"
end