import java.util.Scanner;

public class Main {

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

}

}