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.Linq;
using System.Collections;
using System.Collections.Generic;
using System.Text;


class Program
{
    static void Main(string[] args)
    {
        // 入力
        //var s = Console.ReadLine();
        var n = long.Parse(Console.ReadLine());
        char[] s = Console.ReadLine().ToCharArray();

        var ans = 0;
        var b = 0;
        var w = 0;
        for (int i = 0; i < n - 1; i++)
        {
            if (s[i] == '#')
            {
                b++;
                if (s[i + 1] == '.')
                {
                    var tmp = 0;
                    for (int k = i + 1; k < n; k++)
                    {
                        if (s[k] == '.') w++;
                        else
                        {
                            tmp = k;
                            break;
                        }
                    }

                    if (b > w)
                    {
                        ans += w;
                        i = tmp;
                        w = 0;
                    }
                    else 
                    {
                        ans += b;
                        b = 0;
                    }

                   
                }
            }
        }


        // 出力
        Console.WriteLine(ans);
    }
}