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 PHP (5.6.30) (judge verdict: Wrong Answer)

<?php
fscanf(STDIN, "%d",$cnt);
fscanf(STDIN, "%s",$moji);;

$mc=0;
$aru=true;
/*
for($i=0;$i<$cnt;$i++){
	echo substr($moji,$i,2)."\n";
}
*/

while($aru){
	for($i=0;$i<$cnt-1;$i++){
		$ab=substr($moji,$i,2);
		$check=0;
		if($ab=="#."){
			$moji=substr($moji,0,$i-1)."##".substr($moji,$i,strlen($moji)-$i-1);
			$mc++;
			$check++;
		}
	}
	if($check==0){
		$aru=false;
	}
}
echo $mc;
?>