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.chomp.to_i
s = gets.chomp

if s.count("#") == 0 then
  puts 0
  exit 0
end

tmp_i = 0
count = 0
# 右からみて最初に出てくる.を見つける, それ以降を全部#にする
n.times do |i|
  if s[s.length - i - 1] == "." then
    count = 1
    tmp_i = i
    break
  end
end

# 右からみて最初に出てくる.を見つける, それ以前を全部.にする
n.times do |i|
  next if i <= tmp_i
  if s[s.length - i - 1] == "." then
    count += s[0..(s.length-i-1)].count("#")
    break
  end
end

puts count