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.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.PrintWriter;

public class Main {
    public static void main(String[] args) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        PrintWriter out = new PrintWriter(System.out);
        int N = Integer.parseInt(br.readLine());
        String S = br.readLine();
        int start = S.indexOf("#");
        int end = S.lastIndexOf(".");
        if (start < 0 || end < 0 || start > end) {
            out.println(0);
            out.close();
        } else {
            String s = S.substring(start, end + 1);
            int ans1 = 0;
            int ans2 = 0;
            for (int i = 0; i < s.length(); i++) {
                if ('.' == s.charAt(i)) {
                    ans1++;
                }
                if ('#' == s.charAt(i)) {
                    ans2++;
                }
            }
            out.println(Math.min(ans1, ans2));
            out.close();
        }
    }
}