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)
    {
        //黒から白に変わるポイントを消すための対処法は次の二通り。

        //最初に黒から白に変わるポイント以降を全部黒にする
        //最後に黒から白に変わるポイント以前を全部白にする

        int N = int.Parse(Console.ReadLine());
        string S = Console.ReadLine();

        int kurosiroIdx = S.IndexOf("#.");
        int lastKurosiro = S.LastIndexOf("#.");

        if (kurosiroIdx < 0)
        {
            Console.WriteLine(0);
            return;
        }

        string target1 = new string(S.Take(kurosiroIdx).ToArray()) + new string(Enumerable.Repeat('#', N - kurosiroIdx).ToArray());
        string target2 = new string(Enumerable.Repeat('.', lastKurosiro + 1).ToArray()) + S.Substring(lastKurosiro + 1);


        var dif1 = target1.Zip(S, (c1, c2) => new { c1, c2 }).Count(x => x.c1 != x.c2);
        var dif2 = target2.Zip(S, (c1, c2) => new { c1, c2 }).Count(x => x.c1 != x.c2);

        Console.WriteLine(Math.Min(dif1, dif2));

    }
}