practice.java

import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        float sum = 0;
        int i = 0;

        Map<Integer, Integer> map = new HashMap<>();
        for (int num = 0; num >= 0;) {
            num = sc.nextInt();
            Integer value = map.get(num);
            map.put(num, (value == null) ? 1 : value + 1);
            
            int freq = map.get(num);
            if (freq > 1) {
                sum += num * freq;
                i += freq;
            }
        }

        if (i == 0) System.out.println("Unqe");
        else System.out.printf("%.2f", sum/i);
    }
}