import java.util.*;
public class Main {
    public static void main(String[] args) {
        int count = 0;
        Scanner scanner = new Scanner(System.in);
        int sum =0;
        double avg;
        while(true)
        {
            int j=scanner.nextInt();
            if(j<=0)break;
            count++;
            sum+=j;
        }
        avg=(double)sum/count;
        System.out.printf("%.2f%n",avg);
    }
}