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
//error_reporting(0);
$N = trim(fgets(STDIN));
$S = trim(fgets(STDIN));
//list($A,$B,$C) =  explode(" ",trim(fgets(STDIN)));

$p = strpos($S,"#");
//最後の白以降の黒
$lp = strrpos($S,".");
if ($p === false) {
  $ret = 0;
}
else {
  $n = substr($S,$p);
  //最初の黒以降の白を全部置き換えるか、
  $n2 = substr($S,0,$lp+1);
  //黒を白に置き換えるか(最後の白以降の黒は置き換えなくていい)
  $ret = min(substr_count($n,"."),substr_count($n2,"#"));
}
printf("%d\n",$ret);