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: Time Limit Exceeded)

n = gets.to_i
srray = gets.split("").map(&:to_s)
answer = []
answer.push(srray.count("."))
i=0
brray = []
crray = srray
answer.push(brray.count("#")+crray.count("."))
while i<n
  brray.push(crray.shift)
  # j=0
  # while j<i+1
  #   brray.push(srray[j])
  #   j+=1
  # end
  # while j>i && j<n
  #   crray.push(srray[j])
  #   j+=1
  # end
  answer.push(brray.count("#")+crray.count("."))
  i+=1
end
puts answer.min