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;
using System.Linq;

namespace VSC
{
    class Program
    {
        static void Main(string[] args)
        {
            int N = int.Parse(System.Console.ReadLine());
            string S = System.Console.ReadLine();
 
            char[] str = S.ToCharArray();

            int K = 0;
            int white = S.Length;
            int black = 0;

              while(true){
                    white = Array.LastIndexOf(str,'.');
                    black = Array.IndexOf(str,'#');
                    if(white == -1 )break;
                    if(black == -1 )break;
                    if(black >= white)break;
                    str = str.Skip(black + 1).ToArray();
                    K++;

                    white = Array.LastIndexOf(str,'.');
                    if(white == -1 )break;
                    if(black >= white)break;
                    str = str.Take(str.Length - (white + 1)).ToArray();
                    K++;
              }
            System.Console.Write(K);
        }
    }
}