import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        //write your code here......
        int sum=0;
        int count=0;
        double avg=0.0;
        while(scan.hasNext())
        {
            int n=scan.nextInt();
            if(n<0)
            {
                break;
            }
            count++;
            sum+=n;
        }
        avg=(double)sum/count;
        System.out.println(String.format("%.2f",avg));
    }
}