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

l = 0
while l < N && s[l] == "." 
  l += 1
end
ans = 0
while l < N
  if s[l] == "."
    ans += 1 
    while l < N && s[l] == "."
      l += 1
    end
  else
    l += 1
  end
end
r = N-1
while r >= 0 && s[r] == "#" 
  r -= 1
end
ans2 = 0
while r >= 0
  if s[r] == "#"
    ans2 += 1 
    while r >= 0 && s[r] == "#"
      r -= 1
    end
  else
    r -= 1
  end
end
p [ans,ans2].min