Что не так?

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));
        int sum = 0;
        int x = 0;

        while (true) {
            String s = reader.readLine();
            int a = Integer.parseInt(s);
            sum = sum + a;
            x = x + 1;
            if (s.equals("-1")) {
                break;
            } double y = sum / x;
            System.out.println(y);
        }
    }
}