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;

namespace AtCoder
{
    class Program
    {
        static void Main(string[] args)
        {
            int N = int.Parse(Console.ReadLine());
            char[] c = Console.ReadLine().ToCharArray();

            if(N == 1)
            {
                Console.WriteLine("0");
                return;
            }

            int[] white = new int[N];

            if (c[0] == '.')
                white[0] = 1;
            else
                white[0] = 0;

            for(int i=1;i<N;i++)
            {
                if (c[i] == '.')
                    white[i] = white[i - 1] + 1;
                else
                    white[i] = white[i - 1];
            }

            int allw = white[N - 1];
            int ans = int.MaxValue;

            for(int i=0;i<N;i++)
            {
                int temp = i + 1 + allw - white[i] * 2;
                if (ans > temp)
                    ans = temp;
            }


            Console.WriteLine(ans.ToString());
        }
    }
}