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 java.util.Collections

import scala.io.StdIn

object Main {
  def main(args: Array[String]) = {
    val N = StdIn.readInt
    val S = StdIn.readLine
    val whites = S.count(c => c == '.')
    val blacks = S.count(c => c == '#')

    var wCnt = 0
    var bCnt = 0
    var ans = Int.MaxValue
    for(i <- 0 until N) {
      if (S.charAt(i) == '.') {
        wCnt += 1
      }
      if (S.charAt(i) == '#') {
        bCnt += 1
      }
      ans = Math.min(ans, (whites - wCnt) + bCnt)
    }
    wCnt = 0
    bCnt = 0
    for(i <- N-1 to 0 by -1) {
      if (S.charAt(i) == '.') {
        wCnt += 1
      }
      if (S.charAt(i) == '#') {
        bCnt += 1
      }
      ans = Math.min(ans, (blacks - bCnt) + wCnt)
    }
    println(ans)

  }
}