package de.codegym.task.task05.task0507;
/*
Arithmetisches Mittel
*/
import java.io.*;
public class Solution {
public static void main(String[] args) throws Exception {
//schreib hier deinen Code
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
int count = 0;
double summe = 0;
while(true){
int a = Integer.parseInt(reader.readLine());
if(a == -1){
double ari = summe / count;
System.out.println(ari);
break;
}else{
summe += a;
count++;
}
}
}
}