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)

io = STDIN
n=io.gets.to_i
s=io.gets.chomp.split(//).chunk_while{|a,b|a==b}.to_a
if s.size==1
  puts 0
elsif s[-1][0]=="#" #右#
  if s[0][0]=="#"
    puts s.select{|ar|ar[0]=="."}.inject(0){|s,ar|s+ar.size}
  else
    puts s.select{|ar|ar[0]=="."}[1..-1].inject(0){|s,ar|s+ar.size}
  end
else  #右.
  if s[0][0]=="#"
    puts [s.select{|ar|ar[0]=="#"}.inject(0){|s,ar|s+ar.size},
          s.select{|ar|ar[0]=="."}.inject(0){|s,ar|s+ar.size}].min
  else
    puts [s.select{|ar|ar[0]=="#"}.inject(0){|s,ar|s+ar.size},
          s.select{|ar|ar[0]=="."}[1..-1].inject(0){|s,ar|s+ar.size}].min
  end
end