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 Java7 (OpenJDK 1.7.0) (judge verdict: Wrong Answer)

import java.util.*;
public class Main{
  public static void main(String arg[]){
    Scanner stdIn = new Scanner(System.in);
    int n = stdIn.nextInt();
    String text = stdIn.next();
    String s[] = text.split("",n);
    
    boolean flag = false;
    int i = 0;
    int ansA = 0;
    int ansB = 0;
    while(i < s.length-1){
      if(s[i].equals("#")){
        ansA++;
        flag = true;
      }
      if(flag){
        if(s[i+1].equals(".")){
          ansB++;
        }
      }
      i++;
    }

    int ans;
    if(ansA < ansB) ans = ansA;
    else ans = ansB;
    System.out.println(ans);
  }
}