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 = (int)trim(fgets(STDIN));
$s = trim(fgets(STDIN));

$cnt = 0;
if ($s[0] === '#') {
	// all b
	for ($i=0; $i < $n; $i++) { 
		$tmp = $s[$i];
		if ($tmp === '.') {
			$cnt += 1;
		}
	}
}else{
	$b_flg = false;
	for ($i=0; $i < $n; $i++) { 
		$tmp = $s[$i];
		if ($tmp === '#') {
			$b_flg = true;
		}
		if ($tmp === '.' && $b_flg) {
			$cnt += 1;
		}
	}
}

echo $cnt;