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.*;
public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    String s = sc.next();
    int w = 0;
    int b = 0;
    int k = 1;
    int l = 1;
    int min = 0;
    if(s.charAt(0)=='.')
      while(k<=n-2&&s.charAt(k)==s.charAt(k+1))k++;
    if(s.charAt(n-1)=='#')
      while(l<=n-1&&s.charAt(n-l)==s.charAt(n-l-1))l++;
    for(int i = 0;i < n;i++){
      if(s.charAt(i)=='#')b++;
      else w++;
    }
    if(s.charAt(0)=='.'&&s.charAt(n-1)=='#')min = Math.min(b-l,w-k);
    else if(s.charAt(0)=='.')min = Math.min(w-k,b);
    else if(s.charAt(n-1)=='#')min = Math.min(w,b-l);
    else min = Math.min(w,b);
    System.out.println(min);
  }
}