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: Accepted)

_=gets.to_i
s=gets.chomp
if s.index('#.').nil?
  puts 0
  exit 0
end
rc = '#'
b = 0
aw = s.count('.')

map = s.split('').map.with_index(1) do |c, mapi|
  b += 1 if c == '#'
  if rc == '.' && c == '#'
    rc = c
    b-1 + (aw - (mapi - b) )
  else
    rc = c
    nil
  end
end

puts (map.compact << s.count('.') << s.count('#')).min