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));
}
}