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.math.*;

class Main{
    
    public static void main(String[] args){
        Scanner in = new Scanner(System.in);
        
        int n = in.nextInt();    
        String s = in.next();
        
        Vector <Integer> vc = new Vector<Integer>();
        Vector <Integer> vpos = new Vector<Integer>();
        
        int ans = 0, ans2 = 0, ans3 = 0, ans4 = 0, ans5 = 0;
        int ch1 = 0;
        int ch2 = 0;
        s+='@';
        if (n != 1){
            for (int i = n - 1; i > -1; --i)
                if (s.charAt(i) == '#')  ++ch1; 
                    else  ++ch2;
                    
            int tmp = 0;
            
            for (int i = n - 1; i > -1; --i)
                if (s.charAt(i) == '.') ++tmp; 
                    else{
                        if (tmp != 0) vpos.add(i);
                        vc.add(tmp);
                        tmp  = 0;
                    }
                
            /*for (int i = n - 1; i > -1; --i){
                if (s.charAt(i) == '#') ++ans3;
                    else break;
            }*/
            if (s.charAt(0) == '#' && s.charAt(1) == '.'){
            int key = 0;
            for (int i = 0; i < n; ++i){
                if (s.charAt(i) == '#') ++ans4;
                    else{
                        ++key;
                        break;
                    }
            }
            for (int i = key + 1; i < n; ++i){
                if (s.charAt(i) == '.') ++ans5;
                    else break;
            }
            }
            ans2 = 0;    
            for (Integer x : vc)
                ans2+=x;
            }
        System.out.print(Math.min(Math.min(ans2, ch1),ans2 - ans5));
    }
}