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# (.NET Core 3.1.201) (judge verdict: Wrong Answer)

using System;
using System.Text;
using System.Collections.Generic;
using System.Collections;
using static System.Math;
using System.Linq;
using static System.Array;

namespace ConsoleApp2
{
    class Program
    {
        static string S;
        static void Main(string[] args)
        {
            var N = long.Parse(Console.ReadLine());
            //va0r NKMR = Console.ReadLine().Split(' ').Select(x => long.Parse(x)).ToArray();
            var S = Console.ReadLine();

            var L = 0;
            var R = N - 1;

            //右から見ていって最初の白を探す．
            for (; R >= 0; R--)
            {
                if (S[(int)R] == '.')
                {
                    break;
                }
            }

            for (; L < N; L++)
            {
                if (S[(int)L] == '#')
                {
                    break;
                }
            }

            var blacK = 0;
            var white = 0;

            for (int i = L; i <= R; i++)
            {
                if (S[(int)i] == '#')
                {
                    blacK++;
                }
                else
                {
                    white++;
                }
            }

            Console.WriteLine(Min(blacK,white));
            
        }
       
        static long Cul(char spi)
        {
            var tmp = S.Split(spi).ToArray();
            long ans = 0;
            foreach (var item in tmp)
            {
                ans = Max(ans, item.Length);
            }
            return ans;
        }
    }


}