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: Runtime Error)

import java.util.*;

class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = Integer.parseInt(sc.next());
    String s = sc.next();
    int[] a;
    a = new int[n];

    String check = "";
    int flg = 0;
    int cnt = 0;
    int scnt = 0;
    int buf = 0;
    int cursor = 0;

    if (s.substring(0,1).equals(".")) {
      cursor++;
      a[0] = 0;
      flg = 1;
    }  
      
    for (int i=1; i<n; i++) {
      check = s.substring(i,i+1);
      if (flg == 0 && check.equals("#")) {
        buf++;
      }
      if (flg == 0 && check.equals(".")) {
        a[cursor] = buf;
        buf = 1;
        flg = 1;
        cursor++;
      }
      if (flg == 1 && check.equals(".")) {
        buf++;
      }
      if (flg == 1 && check.equals("#")) {
        a[cursor] = buf;
        buf = 1;
        flg = 0;
        cursor++;
      }
    }
    
    if (s.substring(n-1,n).equals(".")) {
      cursor++;
      a[cursor] = 0;
    }  
    
    int min = n;
    int total = 0;
    for (int i=1; i<=cursor; i++) {
	  total = 0;
      flg = 0;
      for (int j=1; j<i; j+=2) {
        total += a[j];
      }
      for (int j=i; j<=cursor; j+=2) {
        if (i%2 == 1 && flg == 0) { j++; flg++; } else { flg++; }
        total += a[j];
      }
      if (total < min) {
        min = total;
      }
    }
    
    System.out.println(min);
  }
}