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 Pascal (FPC 2.6.2) (judge verdict: Accepted)

var a  :char;
    s,t  :array[0..200010]of integer;
    n,i,j,k,ans  :integer;
    
function min(a,b:integer):integer;
begin
  if a>b then min:=b
  else min:=a
end;

begin
  readln(n);
  s[0]:=0;
  for i:=1 to n do begin
    read(a);
    if a='#' then s[i]:=s[i-1]+1
    else s[i]:=s[i-1];
    end;
  ans:=210000;
  for i:=0 to n do t[i]:=s[i]+n+s[i]-i-s[n];
  for i:=0 to n do ans:=min(ans,t[i]);
  writeln(ans)
end.