import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);

        //write your code here......
        double sum =0;
        int count = 0;
        while(true){
            int n = scan.nextInt();
            if (n<0) break;
            sum +=n;
            count++;
        }

        System.out.println(String.format("%.2f",sum/count));
        //输出格式为:System.out.println(String.format("%.2f",avg));
        

    }
}

挺简单的