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 Common Lisp (SBCL 1.1.14) (judge verdict: Wrong Answer)

(defun solve (rocks)
  (let ((found nil))
    (loop :for rock :across (reverse rocks)
          :when (char= rock #\.)
            :do (setf found t)
          :count (and found (char= rock #\#)))))

(defun reverse-solve (rocks)
  (let ((found nil))
    (loop :for rock :across rocks
          :when (char= rock #\#)
            :do (setf found t)
          :count (and found (char= rock #\.)))))

(defun main ()
  (read)
  (let ((rocks (read-line)))
    (format t "~A~%" (min (reverse-solve rocks) (solve rocks)))))

(main)