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)

#!/usr/bin/ruby
# encoding: utf-8

N = gets.to_i
S = gets.chomp

S2 = S.dup

th = 0

(0..N-1).each do |i|
  if S[i] == '#' && S[i+1] == '.' then
    th = i+1
    break
  end
end

# 0～i+1 までの'#'の数と
# i+2 ～ N-1 までの'.'の数をカウントすればよい。

ans1 = 0
ans2 = 0

(0..th).each do |i|
  if S[i] == '#' then 
    S2[i] = '.'
    ans1 += 1

#    if S2 == S2.sort.reverse then
#      break
#    end

  end
end

if S2 == S2.split.sort.reverse then
  pus ans1
  exit
end

if th+1 <= N-1 then
  (th+1..N-1).each do |i|
    if S[i] == '.' then 
      ans2 += 1
    end
  end
end

if th == 0 then
  puts 0
elsif 
  puts ans1+ans2
end