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;

namespace C___Stones
{
    class Program
    {
        static void Main(string[] args)
        {
            var N = int.Parse(Console.ReadLine());
            var S = Console.ReadLine().ToCharArray();
            char[] b_arr = new char[N], w_arr = new char[N];
            Array.Copy(S, b_arr, N);
            Array.Copy(S, w_arr, N);
            int b_count = 0, w_count = 0;

            for (int i = 0; i < N - 1; i++)
            {
                if ((b_arr[i] == '#') && (b_arr[i + 1] == '.'))
                {
                    b_arr[i + 1] = '#';
                    b_count++;
                }

            }

            for (int i = N - 1; i > 0; i--)
            {
                if ((w_arr[i] == '.') && (w_arr[i - 1] == '#'))
                {
                    w_arr[i - 1] = '.';
                    w_count++;
                }
            }

            Console.WriteLine(Math.Min(b_count, w_count));
        }
    }
}