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 static System.Console;
using static System.Math;

namespace At
{
    class Program
    {
        static void Main(string[] args)
        {
            var n = ReadInt();
            var s = Read();

            var black = CountChar(s, "#");
            var white = CountChar(s, ".");

            if (black == n || white == n)
            {
                WriteLine(0);
                return;
            }

            var a1 = s.IndexOf("#");
            //WriteLine(a1);
            var s1 = s.Substring(a1,n-a1);
            s = s1;


            if (CountChar(s, "#") > CountChar(s, "."))
            {
                var a = s.IndexOf("#");
                WriteLine((s.Length - s.Replace(".", "").Length) - a);
            }
            else
            {
                var a = s.LastIndexOf(".");
                WriteLine((s.Length - s.Replace("#", "").Length) - (a - s.Length + 2));
            }
        }
        public static int CountChar(string s, string c)
        {
            return s.Length - s.Replace(c.ToString(), "").Length;
        }

        private static string Read() { return ReadLine(); }
        private static string[] Reads() { return (Read().Split()); }
        private static int ReadInt() { return int.Parse(Read()); }
        private static long ReadLong() { return long.Parse(Read()); }
        private static double ReadDouble() { return double.Parse(Read()); }
        private static int[] ReadInts() { return Array.ConvertAll(Read().Split(), int.Parse); }
        private static long[] ReadLongs() { return Array.ConvertAll(Read().Split(), long.Parse); }
        private static double[] ReadDoubles() { return Array.ConvertAll(Read().Split(), double.Parse); }
    }
}