package com.javarush.task.task05.task0507;

/*
Среднее арифметическое
*/

public class Solution {
    public static void main(String[] args) throws Exception {
    int x = 0;
    int a = 0;
    int b = 0;
    while (x != -1) {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        String s = reader.readLine();
        x = Integer.parseInt(reader.readLine(s));
        if (x != -1) {
            a = a + x;
            b = b + 1;
        }
    }
        System.out.println(a / b);
    }
}