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.Linq;
using System.Collections.Generic;

using E = System.Linq.Enumerable;

public class Program
{
    public static void Main()
    {
        var n = int.Parse(Console.ReadLine());
        var s = Console.ReadLine().Trim().Select(x => x == '.' ? 0 : 1).ToArray();

        var sum = new int[s.Length + 1][];
        sum[0] = new int[2];
        for (int i = 1; i < sum.Length; i++)
        {
            sum[i] = new int[sum[i - 1].Length];
            for (int j = 0; j < sum[i].Length; j++)
            {
                sum[i][j] = sum[i - 1][j];
            }
            sum[i][s[i - 1]]++;
        }

        var minimum = int.MaxValue;
        for (int i = 1; i < sum.Length; i++)
        {
            var w = sum.Last()[0] - sum[i][0];
            var b = sum[i][1]; // - sum.First()[1];
            minimum = Math.Min(minimum, w + b);
        }
        Console.WriteLine(minimum);
    }
}