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: Accepted)

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

$res = $white = substr_count($s, '.');

// .が1つもない || 全て. || #の右側に.が存在しない場合は変更する必要ないので0を返す
if ($white === 0 || $white === $n || preg_match('/^\.*#*$/', $s)) {
    echo 0;
    return;
}

$black = 0;
for ($i = 0; $i < $n;$i++) {
    if ($s[$i] === '#') {
        $black++;
    } else {
        $white--;
    }
    $res = min($res, $black + $white);
}

echo $res > 0 ? $res : 0;