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
$n=trim(fgets(STDIN));
$s=trim(fgets(STDIN));
$c=array_count_values(str_split($s));
if(isset($c["."])){
  $ans=min($n-$c["."],$c["."]);
}else{
  $ans=min($n-$c["#"],$c["#"]);
}
if($ans==0){
  echo 0;
}else{
  $key=array_keys(str_split($s),".");
  $i=1;
  foreach($key as $k=>$v){
    $ans=min($ans,$v+1+count($key)-$i*2);
    ++$i;
  }
  echo $ans;
}