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 test
{
    class Program
    {
        static void Main(string[] args)
        {
            var N = ReadInt();
            var S = Read();
            var white = 0;
            var black = N - 1;
            var change = false;
            for (int i = 0; i < N; i++)
            {
                if (S[i] != '.')
                {
                    white = i;
                    change = true;
                    break;
                }
            }
            if (!change)
            {
                Console.WriteLine(0);
                return;
            }
            change = false;
            for (int i = N - 1; i >= 0; i--)
            {
                if (S[i] != '#')
                {
                    black = i;
                    change = true;
                    break;
                }
            }
            if (!change)
            {
                Console.WriteLine(0);
                return;
            }
            var cntW = 0;
            var cntB = 0;
            for (int i = white; i <= black; i++)
            {
                if (S[i] == '#') cntW++;
                else if (S[i] == '.') cntB++;
            }

            Console.WriteLine(Math.Min(cntW, cntB));
            Console.ReadLine();
        }

        static string Read() { return Console.ReadLine(); }
        static int ReadInt() { return int.Parse(Read()); }
        static long ReadLong() { return long.Parse(Read()); }
        static int[] ReadArrayInt() { return Read().Split(' ').Select(s => int.Parse(s)).ToArray(); }
        static long[] ReadArrayLong() { return Read().Split(' ').Select(s => long.Parse(s)).ToArray(); }
    }
}