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: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp5
{

    class Program
    {
        static void Main(string[] args)
        {

            int N = int.Parse(Console.ReadLine());
            string S = Console.ReadLine();
            int res = 0;
            int WP = 0;


            for (int i=0; i<N; i++)
            {
                if (S[i] == '#')
                {
                    res++;
                }

            }

            int ans = res;
           
            for(int i=N-1; i>=0; i--)
            {
                if(S[i] == '#')
                {
                    res = res - 1 + WP;
                    WP = 0;
                    if(res < ans)
                    {
                        ans = res;
                    }
                }
                else
                {
                    WP++;
                }
                
            }

            Console.WriteLine(ans);
        }
    }
}