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;

namespace T119c
{
    class Program
    {
        static void Main(string[] args)
        {
            //int N = int.Parse(Console.ReadLine());
            Console.ReadLine();
            string S = Console.ReadLine();

            List<char> cl = new List<char>(S);

            int countkuro = 0;
            int countsiro = 0;

            int startindex = 0;
            //黒に変える場合
            //黒の右に白があると嫌なので、左の白は無視できる
            int findex = cl.FindIndex(startindex, c => c == '#');

            //....####....####....
            //#4
            //.8
            //#12
            //.16
            //#-1

            for (; ; )
            {
                if(findex == -1)
                {
                    break;
                }
                startindex = findex;
                findex = cl.FindIndex(startindex, c => c == '.');

                if (findex == -1)
                {
                    break;
                }
                startindex = findex;
                findex = cl.FindIndex(startindex, c => c == '#');

                if (findex == -1)
                {
                    countkuro += cl.Count - startindex;
                    break;

                }
                else
                {
                    countkuro += findex - startindex;

                }

            }

            //白に変える場合
            //最後の黒だけ無視できる
            //..##..##..##
            //#2
            //.4
            //#6
            //.8
            //#10
            //.-1
            //Ans 4

            startindex = 0;
            findex = 0;

            for (; ; )
            {
                startindex = findex;
                findex = cl.FindIndex(startindex, c => c == '#');

                if (findex == -1)
                {
                    break;
                }

                startindex = findex;
                findex = cl.FindIndex(startindex, c => c == '.');

                if (findex == -1)
                {
                    break;

                }
                else
                {
                    countsiro += findex - startindex;

                }

            }



            if (countkuro < countsiro)
            {
                Console.WriteLine(countkuro);
            }
            else
            {
                Console.WriteLine(countsiro);
            }

//            Console.ReadLine();
        }
    }
}