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 Scala (2.11.7) (judge verdict: Wrong Answer)

object Main {
  def main(args: Array[String]): Unit = {
    scala.io.StdIn.readLine()
    @scala.annotation.tailrec
    def go(l: List[Char], bf: List[Char]): List[Char] =
      if (l.isEmpty) bf
      else if (l.head == '#') go(l.tail, bf)
      else l ++ bf
    val line = go(scala.io.StdIn.readLine().reverse.toList, Nil) ++ "#."
    println(line.groupBy(identity).values.map(_.size - 1).reduce((a, b) => if (a > b) b else a))
  }
}