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
fscanf(STDIN, '%d', $n);
fscanf(STDIN, '%s', $s);

$white = substr_count($s, '.');
if ($white === 0 || $white === $n) {
    echo 0;
    return;
}
$blackCount = substr_count($s, '#');
$blackFirstPos = strpos($s, '#');
$blackLastPos = strrpos($s, '#');
if ($blackFirstPos === 0) {
    // 先頭が黒の場合は、白の数か黒の数が少ない方を出力する
    echo min(($n - ($n - $white)), $blackCount);
} elseif ($blackCount === 1 && $blackLastPos === $n - 1) {
    // 黒が1つしかない && 末尾が黒
    echo 0;
} else  {
    //　先頭が黒ではない && 末尾が黒ではない場合
    echo min($n - ($blackFirstPos + $blackCount), $blackCount);
}