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: Accepted)

n = gets.chomp
s = gets.chomp.split(//)

ans = 10000000

a = 0
b = s.count{|e| e == '.'}

s.size.times do |i|
  if s[i] == '#'
    a += 1
  else
    b -= 1
  end
  count = a + b
  # p count
  ans = [ans, count].min
end



200000.times do
  s.shift if s[0] == '.'
  s.pop if s[-1] == '#'
end

a = 0
b = 0

s.each do |c|
  a += 1 if c == '#'
  b += 1 if c == '.'
end

puts [ans, a, b].min