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.Scanner;
public class Main{
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		String s = sc.next();
		long ans=Long.MAX_VALUE;
		long[] b=new long[n];
		if(s.charAt(0)=='#'){
			b[0]=1;
		}
		for(int i = 1; i<s.length(); i++){
			if(s.charAt(i)=='#'){
				b[i]=b[i-1]+1;
			}else{
				b[i]=b[i-1];
			}
		}
		for(int i = 0; i<s.length(); i++){
			ans=Math.min(ans,2*b[i]+s.length()-i-1-b[s.length()-1]);
		}
		ans=Math.min(ans,s.length()-b[s.length()-1]);
		System.out.println(ans);
	}
}