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-mcs 6.8.0.105) (judge verdict: Wrong Answer)

using System;
using System.Text;
using System.Collections.Generic;
using static System.Math;
using System.Linq;
using static System.Array;

namespace ConsoleApp2
{
    class Program
    {
        static long N;
        static long K;
        static long[] ans;
        static long mod = 1000000007;
        static void Main(string[] args)
        {
            var N = long.Parse(Console.ReadLine());
            var S = Console.ReadLine();
            long bl = 0;
            for(int i = 0; i < N; i++){
                if(S[i] != '.'){
                    bl = i;
                    break;
                }
            }

            long wh = 0;
            for (int i = (int)N - 1; i >= 0; i--)
            {
                if(S[i] == '.'){
                    wh = i;
                    break;
                }
            }

            long black = 0;
            long white = 0;
            long len = wh - bl +1;

            for(; bl <= wh; bl++){
                if(S[(int)bl] == '.'){
                    black++;
                }else{
                    white++;
                }
            }
            //Console.WriteLine(black);
            Console.WriteLine(len - Math.Max(black,white));
        }
    }    
}