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
$n = trim(fgets(STDIN));  
$str = trim(fgets(STDIN));

$beforeCount = substr_count($str, '#.');
if ($beforeCount === 0 ) {
	echo 0, PHP_EOL;
  	exit();
}

$strs = str_split($str);

//black to white
$bToWCount = 0;
for ($i = 0; $i < $n - 1; $i++) {
	if($strs[$i] === '#') {
    	$bToWCount++;
    }
}

//white to black
$wToBCount = 0;
for ($i = 0; $i < $n; $i++) {
	if($strs[$i] === '.') {
    	$wToBCount++;
    }
}

echo min($bToWCount, $wToBCount), PHP_EOL;