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 T1BC2019_C
{
    class Program
    {
        static void Main(string[] args)
        {
            int n = int.Parse(Console.ReadLine());
            string s = Console.ReadLine();

            bool zeroFlag = true;
            int count = 0;
            int zeroCount = 0;
            int blackCount = 0;
            int lastBlackCount = 0;

            for (int i = 0; i < n; ++i)
            {
                bool whiteFlag = s[i] == '.';

                if (whiteFlag)
                {
                    if (zeroFlag)
                    {
                        ++zeroCount;
                    }
                    else
                    {
                        ++count;
                    }

                    lastBlackCount = 0;
                }
                else
                {
                    zeroFlag = false;

                    ++blackCount;
                    ++lastBlackCount;
                }
            }

            if (lastBlackCount != 0 && n - zeroCount == lastBlackCount && blackCount == lastBlackCount)
            {
                count = 0;
            }
            else
            {
                blackCount -= lastBlackCount;

                if (blackCount < count)
                {
                    count = blackCount;
                }
            }   

            Console.WriteLine("{0}", count);
        }
    }
}