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.chop.to_i
S = gets.chop

a=0
b=0
for num in 0..N-1 do
  if S[num] == ?# and S[num+1] == ?.
    a = S.slice(num + 1 .. N-1).count('.')
    break
  end
end

for num in 0..N-2 do
  if S[N - num - 2] == ?# and S[N - num - 1] == ?.
    b = S.slice(0..N - num - 2).count('#')
    break
  end
end

p (a<b)?a:b