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: Runtime Error)

n = gets.to_i
s = gets.chomp.split("")

if s.count("#") == 0 || s.count(".") == 0
   puts 0
else
   f_b = s.index("#")
   bf_b = s[0..f_b]
   af_b = s[f_b+1..-1]

   if af_b.length == 0 #_ #^
      puts 0
   elsif bf_b.length == 1 #_ ~#
      if s.count("#") > s.count(".")
         puts s.count(".")
      else
         puts s.count("#")
      end
   else

      if af_b.count("#") >= af_b.count(".")
         last_w = af_b.rindex(".")
         middle = af_b[0..last_w]
         if middle.count("#") >= af_b.count(".")
            puts middle.count(".")
         else
            puts middle.count("#")+1
         end
#        puts af_b.count(".")
      else
         puts af_b.count("#")#+1
      end
   end
end