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 {
	public static void main(String[] args) {
		Scanner stdIn=new Scanner(System.in);
		int N=stdIn.nextInt();
		String S=stdIn.next();
		int black[]=new int[N];
		int white[]=new int[N];
		int z=0,b=0,w=0,min=N*2;
		while(z<N){
			if(S.charAt(z)=='#')
				w++;
			if(S.charAt(N-1-z)=='.')
				b++;
			white[z]=w;
			black[N-1-z]=b;
			z++;
		}z=0;b=0;
		while(z<N){
			if(z==0)
				b=black[z];
			if(z==N-1)
				b=white[z];
			if(z!=0&&z!=N-1){
				b=white[z]+black[z+1];
			}
			if(b<min)
				min=b;
			z++;
		}
		System.out.println(min);
	}
}