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;
using System.Text;
using System.Threading.Tasks;

namespace tenka1_2019_c
{
    class Program
    {
        static void Main(string[] args)
        {
            var N = decimal.Parse(Console.ReadLine());
            var S = Console.ReadLine();
            int b = 0;
            int w = 0;

            var fb = S.IndexOf("#");

            if (fb < 0)
                //全白
                Console.WriteLine(0);
            else
            {
                //初出の黒以降にある色をカウント
                for (int i = fb; i < N; i++)
                    if (S[i] == '#')
                        b++;
                    else
                        w++;

                Console.WriteLine(Math.Min(b, w));

            }
          
        }
    }
}