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;
using System.Text;
using System.Threading.Tasks;

class Program
{

    static void Main(string[] args)
    {
        ProblemC();
    }
  
	static void ProblemC()
    {
        System.Console.ReadLine();//N
        bool[] S = System.Console.ReadLine().Select(
            (c) => {
                if(c == '#')
                {
                    return true;
                }
                else
                {
                    return false;
                }
            }).ToArray();

        bool firstFound = false;
        int countB = 0;
        int countWAfterB = 0;
        int lastW = 0;
        for (int i = 0; i < S.Length; i++)
        {
            if (S[i])
            {
                countB++;
                if (!firstFound)
                {
                    firstFound = true;
                }
            }
            else
            {
                if (firstFound) 
                { 
                    countWAfterB++;
                }
                lastW = i;
            }
        }

        int ans = 0;
        if (!firstFound)
        {
            // 黒なし
            ans = 0;
        }
        else if(countWAfterB < countB) 
        {
            ans = countWAfterB;
        }
        else
        {
            ans = countB;
        }
        System.Console.WriteLine(ans.ToString());

    }
}