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 Java8 (OpenJDK 1.8.0) (judge verdict: Wrong Answer)

import java.util.Scanner;

public class Main {
  final static char WHITE = '.';
  final static char BLACK = '#';

  public static void main (String[] args) {
    Scanner in = new Scanner(System.in);

    while (in.hasNext()) {
      int N = in.nextInt();
      char[] S = in.next().toCharArray();
  
      int i = 0;
      while (i < S.length && S[i] == WHITE) {
        ++i;
      }

      int change = 0;
      while (i < S.length) {
        int countBlack = 0;
        while (i < S.length && S[i] == BLACK) {
          ++countBlack;
          ++i;
        }

        int countWhite = 0;
        while (i < S.length && S[i] == WHITE) {
          ++countWhite;
          ++i;
        }

        if (countWhite > 0) {
          change += Math.min(countBlack, countWhite);
        }
      }

      System.out.println(change);
    }
  }
}