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 = Integer.parseInt(sc.next());
		
		String s = sc.next();
		
		
		int first = -1;
		int cnt = 0;
		boolean white = false;
		
		for(int i = 0 ; i < n ;i++) {
			if(first == -1 && s.charAt(i) == '#') {
				first = 1;
			}
			else if(first == 1 && s.charAt(i) == '.') {
				if(!white) {
				white = true;
				}
			}
			else if(first == 1 && white && s.charAt(i) == '#') {
				cnt++;
				white = false;
			}
		}
		if(white) {
			cnt++;
		}
		
		System.out.println(cnt);
	}
}