import java.util.Scanner; import java.lang.String;

public class Main {

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

    //write your code here......
    int m = 0;
    int i = 0;
    //一定要是double类型,不然会发生截断,导致小数点后出错。
    double sum = 0.0;
    while((m = scan.nextInt()) > 0){
        sum += m;
        i++;
    }
    double avg = sum/i;
    //输出格式为:System.out.println(String.format("%.2f",avg));
    System.out.println(String.format("%.2f",avg));

}

}