import java.util.Scanner;

public class Main {

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

    //write your code here......
    double avg;
    int count = 0;
    double sum = 0;
    while(scan.hasNextInt()){
        int num = scan.nextInt();
        if(num<0)break;
        sum += num;
        count++;
    }
   
    avg = sum/count;
    System.out.println(String.format("%.2f",avg));

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

}

}