package com.javarush.task.task05.task0507;

import java.io.BufferedReader;
import java.io.InputStreamReader;

/*
Среднее арифметическое
*/

public class Solution {
    public static void main(String[] args) throws Exception {
          BufferedReader reader =new BufferedReader(new InputStreamReader(System.in));
        double sum = 0;
        double num = 0;
        float sr =  0;

        while(true) {
            String g = reader.readLine();
            double a = Integer.parseInt(g);

            if (a == -1)
            break;

            num++;
            sum+=a;
            sr=sum/num;


        }
        System.out.println(sr);//напишите тут ваш код
    }
}