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());
            string s = ReadLine();
            //先頭白を取り除く
            for (int i = 0; i < N; i++)
            {
                if (s[i] == '#')
                {
                    s = s.Substring(i, N-i);
                    break;
                }
            }
            //後方黒を取り除く
            for (int i = s.Length-1 ; 0 < i; i--)
            {
                if (s[i] == '.')
                {
                    s = s.Substring(0, i+1);
                    break;
                }
            }
            //白と黒数える
            int kuro = 0; int shiro = 0;
            for (int i = 0; i < s.Length; i++)
            {
                if (s[i] == '.')
                {
                    shiro++;
                }
                else
                {
                    kuro++;
                }
            }
            WriteLine(
                Min(kuro,shiro)
                );
        }
    }
}