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 C# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
class Program{
  static void Main(string[] args){
    int n = int.Parse(Console.ReadLine());
    string s = Console.ReadLine();
    int w=-1, b=n;
    for(int i=0;i<n;i++){
      if(s[i]=='#'){w=i-1;break;}
    }
    for(int i=n-1;i>-1;i--){
      if(s[i]=='.'){b=i+1;break;}
    }
    string t = s;
    if(b<n){t=t.Remove(b);}
    if(w>-1){t=t.Remove(0,w+1);}
    int u=t.Length;
    int x=t.Replace(".","").Length;
    int y=u-x;
    Console.WriteLine(u>2*x?x:u-x);
  }
}