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.IO;
using static System.Console;
using static System.Math;

namespace AtCodeeeer
{
    class AtCOOOOOOOOOOOder
    {
        static void Main(string[] args)
        {
            int N = int.Parse(ReadLine());
            var s = ReadLine();

            //初期処理
            int kuro = 0;
            int shiro = 0;
            var tmp = s[0];
            bool kuroFlug = false;
            bool shiroFlug = false;


            for (int i = 1; i < N; i++)
            {
                if (tmp == '#' && s[i] == '.')
                {
                    kuro++;
                    kuroFlug = true;
                }

                if (kuroFlug && s[i] == ',')
                {
                    kuro++;
                }

                if (tmp ==  '.' && s[i] == '#')
                {
                    kuroFlug = false;
                }
                //shiro
                if (tmp == '.' && s[i] == '#')
                {
                    shiro++;
                    shiroFlug = true;
                }

                if (shiroFlug && s[i] == '#')
                {
                    shiro++;
                }

                if (tmp == '#' && s[i] == '.')
                {
                    shiroFlug = false;
                }

                tmp = s[i];
            }
            WriteLine(Min(kuro,shiro));
        }
    }
}