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 AtCoder.Tenka1._2019Beginner
{
    class C
    {
        static void Solve()
        {
            int n = int.Parse(Console.ReadLine());
            string s = Console.ReadLine();
            
            //初期配置の最も右の白の位置を取得
            int r = s.Length-1;
            while (r >= 0 && s[r] == '#')
                r--;

            //初期配置の最も左の黒の位置を取得
            int l = 0;
            while (l < s.Length && s[l] == '.')
                l++;

            if (r < 0 || l == s.Length)
            {
                Console.WriteLine(0);
                return;
            }

            int bc = 0;
            for(int i = 0; i < r; i++)
            {
                if (s[i] == '#')
                    bc++;
            }

            int wc = 0;
            for(int i = l; i < s.Length; i++)
            {
                if (s[i] == '.')
                    wc++;
            }

            Console.WriteLine(bc < wc ? bc : wc);
        }

        static void Main(string[] args)
        {
            Solve();
        }
    }
}