/**
 * This program demonstrates reading multiple data values.  A trailer value is
 * used to signalthe end of input.
 */

import java.util.Scanner;

public class AddNumbers {

    public static void main( String[] args ) {

        Scanner inp = new Scanner( System.in);

        System.out.print("enter data values (negative integer terminates input):");
        int data = inp.nextInt();
        int sum = 0;
        int numData = 0;
        while( data >= 0 ) {
            ++ numData;
            sum += data;
            data = inp.nextInt();
        }

        double avg = (double)sum / numData;
        System.out.println(avg);

    }

}