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 => in}

object Main extends App {
  val n = in.readInt
  val s = in.readLine.toArray
  val rs = s.reverse
  var cnt1 = 0
  var cnt2 = 0

  for(i <- 0 until n-1) {
    if(s(i)=='#' && s(i+1) == '.'){
      cnt1 += 1
      s(i+1) = '#'
    }
    if(rs(i) == '.' && rs(i+1) == '#'){
      cnt2 += 1
      rs(i+1) = '.'
    }
  }

  val ans = cnt1 min cnt2
  println(ans)
}