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;

namespace Tenka1BC2019_C
{
    class Program
    {
        static void Main(string[] args)
        {
            var N = int.Parse(Console.ReadLine());
            var S = Console.ReadLine();

            var ans = int.MaxValue;
            var lb = 0;
            var lw = 0;
            var rb = S.Where(x => x == '#').Count();
            var rw = S.Length - rb;

            if (rb + lb == 0 || lw + rw == 0)
            {
                Console.WriteLine(0);
                return;
            }

            for (int i = 0; i < S.Length; i++)
            {
                if (S[i] == '.')
                {
                    lw++;
                    rw--;
                }
                else
                {
                    ans = Math.Min(ans, lb + rw);

                    lb++;
                    rb--;
                }
            }

            Console.WriteLine(ans);
        }
    }
}