package com.javarush.task.task05.task0507;
/*
Среднее арифметическое
*/
import java.io.*;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.ArrayList;
public class Solution {
public static void main(String[] args) throws Exception {
ArrayList<Integer> arr = new ArrayList<Integer>();
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
int i = 1;
while (i != -1){
i = Integer.parseInt(reader.readLine());
arr.add(i);
}
double sum = 0;
int nums = 0;
for (int j = 0; j <arr.size() ; j++) {
if (arr.get(j) != -1){
sum = sum + arr.get(j);
nums ++;}
}
//double k = sum;
double result = 0;
result = sum/nums;
System.out.printf("%.1f", result);
// System.out.println(result);
}
}