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: Accepted)

import scala.io.StdIn

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

  def solve2(s: String): Int = {
    var min = s.count(_=='.')
    var ret = min
    s.reverse.dropWhile(_ == '#').reverse.foreach ({
      v => v match {
        case '#' =>  min = min + 1; ret = ret.min(min)
        case '.' => min = min - 1; ret = ret.min(min)
      }
    })

    ret
  }

  
  println(solve2(s))


}