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) throws Exception {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        String s = sc.next();
        
        int c1 = check(s, 0);
        int c2 = check(s, 1);
        System.out.println(c2 == s.length() ? "0" : c1 > c2 ? c2 : c1);
    }
    
    private static int check(String s, int ver) {
        char[] a = s.toCharArray();
        int c = 0;
        boolean check = false;
        if (ver == 0) {
            for (int i=0; i < a.length; i++) {
                if (a[i] == '#') check = true;
                if (a[i] == '.' && check) c++;
            }
        } else {
            for (int i=a.length-1; i >= 0; i--) {
                if (a[i] == '.') check = true;
                if (a[i] == '#' && check) c++;
            }
        }
        return c;
    }
}