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 java.util.Scanner

import scala.collection.mutable.ArrayBuffer

object Main {
  def read() = {
    val sc = new Scanner(System.in)
    val n = sc.nextInt()
    val s = sc.next()
    //val h = for (_ <- 0 until n) yield sc.nextInt()
    (n,s)
  }
  case class RunLengthElem[T](nRepeats: Int, elem: T)

  def compressRunLength[T](s: IndexedSeq[T]): IndexedSeq[RunLengthElem[T]] = {

    var currentChar = s(0)
    var currentCount = 1
    val buf = ArrayBuffer.empty[RunLengthElem[T]]
    for (i <- 1 until s.length) {
      if (currentChar == s(i)) {
        currentCount += 1
      } else {
        buf.append(RunLengthElem(currentCount, currentChar))
        currentChar = s(i)
        currentCount = 1
      }
    }
    buf.append(RunLengthElem(currentCount, currentChar))
    buf.toIndexedSeq
  }


  def solve(n: Int, s: String): Int = {
    val rls = compressRunLength(s)
    val resultWB = {
      val usingRls = if (rls.head.elem == '.') rls.tail else rls
      usingRls.filter(x => x.elem == '.').map(x => x.nRepeats).sum
    }
    val resultBW = {
      val usingRls = if (rls.last.elem == '#') rls.init else rls
      usingRls.filter(x => x.elem == '#').map(x => x.nRepeats).sum
    }
    Math.min(resultWB, resultBW)
  }


  def main(args: Array[String]): Unit = {
    val (n,s) = read()
    println(solve(n,s))
  }

}