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

namespace T119c
{
    class Program
    {
        static void Main(string[] args)
        {
            //int N = int.Parse(Console.ReadLine());
            Console.ReadLine();
            string S = Console.ReadLine();

            List<char> cl = new List<char>(S);

            int countkuro = 0;
            int countsiro = 0;

            int startindex = 0;
            //黒に変える場合
            //黒の右に白があると嫌なので、左の白は無視できる
            int findex = cl.FindIndex(startindex, c => c == '#');

            //....####....####....
            //#4
            //.8
            //#12
            //.16
            //#-1

            for (; ; )
            {
                if(findex == -1)
                {
                    break;
                }
                startindex = findex;
                findex = cl.FindIndex(startindex, c => c == '.');

                if (findex == -1)
                {
                    break;
                }
                startindex = findex;
                findex = cl.FindIndex(startindex, c => c == '#');

                if (findex == -1)
                {
                    countkuro += cl.Count - startindex;
                    break;

                }
                else
                {
                    countkuro += findex - startindex;

                }

            }

            //白に変える場合
            //最後の黒だけ無視できる
            //..##..##..##
            //#2
            //.4
            //#6
            //.8
            //#10
            //.-1
            //Ans 4

            startindex = 0;
            findex = 0;

            for (; ; )
            {
                startindex = findex;
                findex = cl.FindIndex(startindex, c => c == '#');

                if (findex == -1)
                {
                    break;
                }

                startindex = findex;
                findex = cl.FindIndex(startindex, c => c == '.');

                if (findex == -1)
                {
                    break;

                }
                else
                {
                    countsiro += findex - startindex;

                }

            }



            if (countkuro < countsiro)
            {
                Console.WriteLine(countkuro);
            }
            else
            {
                Console.WriteLine(countsiro);
            }

//            Console.ReadLine();
        }
    }
}
