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 sc = new Scanner(System.in);
		int N = sc.nextInt();
		char[] c = new char[N];
		String S = sc.next();
		
		
		for(int i=0; i<N; i++) {
			c[i] = S.charAt(i);
		}
		
		int cnt = 0;
		int bCnt = 0;
		for(int i=0; i<N-1; i++) {
			if(c[i] == '#') bCnt++;
			
			if(c[i] == '#' && c[i+1] == '.') {
				int wCnt = 0;
				int j = i+1;
				while(j < N && c[j] == '.') {
					wCnt++;
					j++;
				}
				
				if(wCnt == bCnt || wCnt > bCnt) {
					//modify white and reset bCnt
					for(int k=i-bCnt+1; k<=i; k++) {
						c[k] = '.';
						cnt++;
						bCnt = 0;
					}
				} else {
					for(int l=i+1; l<i+1+wCnt; l++) {
						c[l] = '#';
						cnt++;
					}
				}
				
			}
		}
		
		System.out.println(cnt);
	}
}