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: Accepted)

using System;
using System.Linq;//リストの使用
using System.Collections.Generic;
using System.Text;//テキストの高速出力に必要
class Program
{
	static void Main()
	{
		int n = int.Parse(Console.ReadLine());
		string s = Console.ReadLine();
    int markOneCountL = 0;//左の.の個数
    int markTwoCountL = 0;//左の#の個数
    int markOneCountR = 0;
    int markTwoCountR = 0;
    long memo = 0;
		long answer = 0;

    for(int i = 0; i < n; i++)
    {
      if(s[i] == '.') markOneCountR++;
      else markTwoCountR++;
    }

    answer = markOneCountR;

    for(int i = 0; i < n; i++)
    {
      if(s[i] == '.')
      {
        markOneCountL++;
        markOneCountR--;
      }else
      {
        markTwoCountL++;
        markTwoCountR--;
      }
      
      answer = Math.Min(answer, markTwoCountL + markOneCountR);
    }

		Console.WriteLine(answer);
	}
}