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 {

    static int firstBlack = 0;
    static int afterBlack = 0;
    static int ans = 0;

    public static void main(String[] args) {

        // input
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        String S = sc.next();

        int count = 0;
        int progress = 200000;
        while (true) {
            firstBlack = 0;
            afterBlack = 0;

            GetAfterBlack(S);

            if (firstBlack == 0) {
                if (count == 0) ans = 0;
                else ans = progress;
                break;
            }
            else if (afterBlack == 0) {
                ans = afterBlack + count;
                break;
            }
            else {
                if (afterBlack + count < progress) {
                    progress = afterBlack + count;
                }
                S = S.substring(firstBlack);
                count++;
            }
        }

        System.out.println(ans);
    }

    public static void GetAfterBlack(String S) {
        // 黒1文字目を取得
        firstBlack = S.indexOf('#') + 1;

        // 後ろの黒の数を取得
        if (firstBlack != 0) {
            for (char str : S.toCharArray()) {
                if (str == '.') {
                    afterBlack += 1;
                }
            }
        }
    }
}