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: Runtime Error)

import java.util.Scanner;

public class Main {
    public static void main(String... args) {
        // 入力
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        String s = sc.next();
        char[] c = s.toCharArray();

        int right = 0;
        int w = 0;
        int b = 0;

        if (c[n - 1] == '.') {
            // 右が白
            for (int i = 0; i < n; i++) {
                if (c[i] == '.') w++;
                else b++;
            }

            if (w > b) System.out.println(b);
            else System.out.println(w);
        } else {
            // 右が黒
            for (int i = n - 1; i >= 0; i--) {
                if (c[i] != '.') right = i + 1;
            }

            if (right == 1) {
                System.out.println(0);
                return;
            }

            for (int i = 0; i <= right; i++) {
                if (c[i] == '.') w++;
                else b++;
            }

            if (w > b) System.out.println(b);
            else System.out.println(w);
        }
    }
}