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)

import scala.io.StdIn

object Main extends App {
  val n  = StdIn.readLine().toInt
  val s  = StdIn.readLine()

  def solve(s: String): Int = {

    if (s.contains(".#")) {
      val rep = s.replace(".#", "a")
      val wi = rep.zipWithIndex.filter(_._1 == 'a').map(_._2)
      var min = Int.MaxValue

      wi.foreach { v =>
        val l = rep.slice(0, v).filter(_ == '#').length
        val r = rep.slice(v + 1, rep.length + 1).filter(_ == '.').length
        if (min > l + r) min = l + r

      }
      min
    } else {
      return 0
    }
  }
  println(solve(s))
}