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));
}
}