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();
        String[] ss = S.split("");

        // 左から見ていく戦法
        int result1 = 0;
        for (int i = 0; i < N-1; i++) {
            if (ss[i].equals("#") && ss[i+1].equals(".")) {
                ss[i+1] = "#";
                result1++;
            }
        }

        ss = S.split("");
        // 右から見ていく戦法
        int result2 = 0;
        for (int i = N-1; i > 0; i--) {
            if (ss[i].equals(".") && ss[i-1].equals("#")) {
                ss[i-1] = ".";
                result2++;
            }

        }

        System.out.println(result1 < result2 ? result1 : result2);
    }
}