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

#puts "now s = #{s}"

new_s = ""
count_1=0
count_2=0
flag = 0

s.length.times do |i|
  if flag==0 && s[i]=="#" then 
    flag = 1
  elsif flag==1 && s[i]=="." then 
    #s[i] = "#"
    count_1+=1 
  end
end
flag = 0

if_count=0
s.length.times do|i|
  if flag==0 &&s[i]=="#" then
    flag=1
    if_count=1
  elsif flag==1&& s[i]=="#" then
    if_count+=1
  elsif flag==1&&s[i]=="." then
    flag=0
    count_2+= if_count
    if_coun=0 
  end 
end

puts [count_1,count_2].min