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: Accepted)

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main {
	public static void main(String args[]) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

		int n = Integer.parseInt(br.readLine());

		String str[] = br.readLine().split("");

		int white[] = new int[n + 1];
		int black[] = new int[n + 1];

		for (int i = 0; i < n + 1; i++) {
			if (i - 1 >= 0) {
				if (str[i - 1].equals("#"))
					black[i] = 1 + black[i - 1];
				else
					black[i] = black[i - 1];
			}
		}

		for (int i = n; i >= 0; i--) {
			if (i + 1 < n) {
				if (str[i + 1].equals("."))
					white[i] = 1 + white[i + 1];
				else
					white[i] = white[i + 1];
			}
		}

		int ans = Integer.MAX_VALUE;

		for (int i = 0; i < n + 1; i++) {
			ans = Math.min(ans, black[i] + white[i]);
		}

		System.out.println(ans);
	}
}