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 PHP7 (7.0.15) (judge verdict: Wrong Answer)

<?php
class MyTest {

    protected $input;

    public function __construct() {
        // # 複数行
        while (!empty($input = fgets(STDIN))) {
            $this->input[] = trim($input);    
        }
    }

    public function run() {
        $n = $this->input[0];
        $str = $this->input[1];
        $count = 0;
        while (strpos($str, '#.') !== false) {
            $str = str_replace('#.', '##', $str);
            $count++;
        }
        
        echo $count;
        
    }
    
}

$test = new MyTest();
$test->run();