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_ary = gets.chomp.to_s.chars
s_ary2 = s_ary.dup

c = 0
s_ary.each_with_index do |v, k|
  if v == "#" && s_ary[k + 1] == "."
    s_ary[k+1] = "#"
    c += 1
  end
end

c2 = 0
s_ary2.each_with_index do |v, k|
  if v == "#" && s_ary2[k + 1] == "."
    s_ary2[k] = "."
    c2 += 1
  end
end

if c > c2
  puts c2
else
  puts c
end