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)

# https://atcoder.jp/contests/tenka1-2019-beginner/tasks/tenka1_2019_c

n = gets.to_i
stones = gets.chomp.chars
res = []

total_black = stones.count('#')
total_white = stones.count('.')
left_black = 0
right_white = total_white

0.upto(stones.size) do |idx|
  res << right_white + left_black
  c = stones[idx]
  left_black += 1 if c == '#'
  right_white -= 1 if c == '.'
end
# p res
puts res.min