package com.javarush.task.task05.task0507;

/*
Среднее арифметическое
*/

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

public class Solution {
    public static void main(String[] args) throws Exception {
        BufferedReader r = new BufferedReader(new InputStreamReader(System.in));
        int n = 0;
        int summ = 0;
        int amount = 0;
        while (n!=-1)
        {
            String nAge = r.readLine();
            n = Integer.parseInt(nAge);
            summ = summ + n;
            amount ++;
            //напишите тут ваш код
        }
        double y = summ/amount;
        System.out.println(y);
    }
}