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.to_i
s = gets.chomp.chars

w = Array.new(n,0)
b = Array.new(n,0)
ans=Array.new
(1...n).each do |i|
	b[i]= if (s[i-1]=='#')
			  b[i-1]+1
		  else
			  b[i-1]
		  end
end
(0...n-1).reverse_each do |i|
	w[i] = if (s[i+1]=='.')
			   w[i+1]+1
		   else
			   w[i+1]
		   end
end
p b,w
(0...n).each do |i|
	ans.push(b[i]+w[i])
end

puts ans.min