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;

class Program
{
    static void Main(string[] args)
    {
        string input = Console.ReadLine();
        int N = int.Parse(input);
        input = Console.ReadLine();
        char[] S= input.ToCharArray();
        int white_num = 0;
        int black_num = 0;
        int conv_num = 0;
        int flag = 0;
        for(int i = 0; i < N; i++)
        {
            if (S[i] == '#')
            {
                white_num++;
                if (flag == 0)
                {
                    flag = 1;
                    conv_num++;
                }
                else if (flag == 1)
                {
                    flag = 2;
                    conv_num++;
                }
            }
            else { black_num++;
                if (flag == 2) { conv_num++; }
            }
        }
        Console.WriteLine(Math.Min(conv_num,Math.Min(white_num,black_num)));
    }
}