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

public class Main {
    static int countBlack(String s){
        int N = s.length();
        int ans=0;
        for(int n=0; n<N; n++) if(s.charAt(n)=='#') ans++;
        return ans;
    }
    static int countWhite(String s){
        return s.length()-countBlack(s);
    }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        String S = sc.next();

        //make it "....####"

        int ans = countWhite(S); //all-black is a possible solution
        int cur = ans;
        for(int n=0; n<N; n++){
            if(S.charAt(n)=='.') cur--;
            else cur++;

            ans = Math.min(ans,cur);
        }

        System.out.println(ans);


    }
}