BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in));
        double summ = 0;
        int count = 0;
        double a = 0;

        while (a != -1)
        {
            a = Integer.parseInt(bufferedReader.readLine());
            if(a!=-1) {
                summ = summ + a;
                count++;
            }
        }
        System.out.println(summ/count);
    }
}