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: Time Limit Exceeded)

_=gets.to_i
s=gets.chomp
if s.index('#.').nil?
  puts 0
  exit 0
end

ia = []
d = 0
loop do
  i = s.index('.#', d)
  break if i.nil?
  ia << i
  d = i+1
end

map = ia.map do |m|
  ps = s[0..m]
  rs = s[m+1..-1]
  ps.count('#') + rs.count('.')
end
puts (map << s.count('.') << s.count('#')).min