public class Main {

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        double result;
        double count=0;
        int i=0;
        while(scan.hasNext()){
            double num=scan.nextDouble();
            if(num<0){
                break;
            }
            count+=num;
            i+=1;
        }
        result=count/(i);
        System.out.println(String.format("%.2f",result));
        
        
        //write your code here......
        

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

    }
}