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;


namespace AtC
{
    class Program
    {
        static void Main(string[] args)
        {
            var N = int.Parse(Console.ReadLine());
            var S = Console.ReadLine();

            char before = '.';
            int count = 0;
            var list = new List<int>();
            for (int i = 0; i < S.Length; i++)
            {
                if (S[i] != before)
                {
                    before = S[i];
                    list.Add(count);
                    count = 1;
                }
                else count++;
            }

            if (count != 0) list.Add(count);

            if (list.Count == 1)
            {
                Console.WriteLine(0);
                return;
            }

            int left = 0, right = 0;
            for (int i = 0; i < list.Count; i += 2)
            {
                right += list[i];
            }

            var counts = new List<int>();

            for (int i = 1; i < list.Count; i += 2)
            {
                counts.Add(left + right);
                left += list[i];
                right -= list[i - 1];
            }

            Console.WriteLine(counts.Min());
        }
    }

    static class EnumerableExtension
    {
        public delegate void Function<in T>(T val);

        public static void ForEach<T>(this IEnumerable<T> enumerable, Function<T> function)
        {
            foreach (var x in enumerable)
            {
                function(x);
            }
        }
    }
}