import java.io.File;
import java.util.Scanner;

public class HW01_1 {

    public static void main(String[] args) {
        Scanner jin = new Scanner(System.in);
        checkTxtSize(jin.nextLine());
        jin.close();
    }

    private static void checkTxtSize(String input) {
        File[] files = new File(input).listFiles();
        double size = 0;
        int count = 0;
        for (int i = 0; i < files.length; i++) {
            if(files[i].isFile()&&files[i].getName().substring(files[i].getName().lastIndexOf(".")+1).equals("txt")){
                size += files[i].length();
                count++;
            }
        }
        System.out.println(String.format("%.2f", size/count));
    }

}