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.Collections.Generic;
using System.Linq;

namespace ConsoleApp
{
    class Program
    {
        static void Main(string[] args)
        {
            var N = int.Parse(Console.ReadLine());
            var S = Console.ReadLine();

            S = new string(S.Reverse().ToArray());
            var w = new List<int>();
            var b = new List<int>();

            var countW = true;
            var count = 0;
            for (int i = 0; i < S.Length; i++)
            {
                if (countW)
                {
                    if (S[i] == '.')
                    {
                        count++;
                    }
                    else
                    {
                        i--;
                        if (count > 0)
                        {
                            w.Add(count);
                        }
                        count = 0;
                        countW = !countW;
                    }
                }
                else
                {
                    if (S[i] == '#')
                    {
                        count++;
                    }
                    else
                    {
                        i--;
                        b.Add(count);
                        count = 0;
                        countW = !countW;
                    }
                }
            }
            if (countW)
            {
                w.Add(count);
            }
            else
            {
                b.Add(count);
            }

            if (w.Count == 0 || b.Count == 0)
            {
                Console.WriteLine(0);
                return;
            }
            
            var sum = new List<int>();
            var tmpSum = 0;
            for (int i = 0; i < w.Count; i++)
            {
                for (int j = 0; j < w.Count; j++)
                {
                    if (j <= i)
                    {
                        if (j < w.Count)
                            tmpSum += w[j];
                    }
                    else
                    {
                        if (j <b.Count)
                            tmpSum += b[j];
                    }
                }
                sum.Add(tmpSum);
            }

            Console.WriteLine(sum.Min());
        }
    }
}