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.to_i
s = gets.chomp
min = 2*(10**5)

kuro=[]
shiro=[]
kuro_count=0
shiro_count=0
n.times do|i|
  if s[i] == "#" then
    kuro_count+=1 
  end
  if s[(n-1)-i] == "." then
    shiro_count+=1
  end
  kuro << kuro_count
  shiro.unshift(shiro_count)
end
#puts "shiro = #{shiro}"
#puts "kuro  = #{kuro}"

(n-1).times do |i|
  m = shiro[i+1] + kuro[i]
  if min>m then
    min=m
  end
end

#puts "min=#{min}"
puts [min,kuro[n-1],shiro[0]].min