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.*;
import java.util.Map.Entry;
 
class Main {
	 static int mod =  (int) (Math.pow(10,9)+7);
//	 static int mod = 998244353;
	 public static void main(String[] args) {
	        Scanner sc = new Scanner(System.in);
	        int N = sc.nextInt();
	        String S = sc.next();
	        char[] c = S.toCharArray();
	        
	        int fcnt=0;
	        for(int i=0;i<N;i++) {
	        	if(c[i]=='#') break;
	        	fcnt++;
	        	
	        }
	        
	        int max=0;
	        int ans=0;
	        int bcnt=0;
	        int wcnt=0;
	        for(int i=fcnt;i<N;i++) {
	        	if(c[i]=='#') {
		        		bcnt++;	        		
	        	} else {
		        		wcnt++;
	        	}
	        	max=Math.max(max, wcnt-bcnt);
	        }
	        
	 		ans=Math.min(bcnt,wcnt)-max;
	        System.out.println(ans);
	 }
	 

}