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.util.*;
import java.lang.*;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		String s = sc.next();
		int[] sum = new int[n];
		if (s.charAt(0) == '#') {
			sum[0] = 1;
		}
		for (int i = 1; i < n; i++) {
			if (s.charAt(i) == '#') {
				sum[i] = sum[i - 1] + 1;
			} else {
				sum[i] = sum[i - 1];
			}
		}
		int min = n - sum[n - 1];
		for (int i = 0; i < n; i++) {
			min = Math.min(sum[i] + (n - i - 1) - (sum[n - 1] - sum[i]), min);
		}
		System.out.println(min);
	}
}