import java.util.*;

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

        int n = sc.nextInt();

        // Constraint check for n
        if (n < 0) {
            System.out.println("Invalid input");
            return;
        }

        ArrayList<Integer> arr = new ArrayList<>();
        boolean hasNegative = false;

        for (int i = 0; i < n; i++) {
            int val = sc.nextInt();
            if (val < 0) {
                hasNegative = true;
            }
            arr.add(val);
        }

        // If any negative number → invalid input
        if (hasNegative) {
            System.out.println("Invalid input");
            return;
        }

        // Sort the ArrayList
        Collections.sort(arr);

        ArrayList<Integer> duplicates = new ArrayList<>();

        // Compare adjacent elements
        for (int i = 0; i < arr.size() - 1; i++) {
            if (arr.get(i).equals(arr.get(i + 1))) {
                // Add only once
                if (!duplicates.contains(arr.get(i))) {
                    duplicates.add(arr.get(i));
                }
            }
        }

        if (duplicates.isEmpty()) {
            System.out.println("No duplicates found");
        } else {
            for (int d : duplicates) {
                System.out.println(d);
            }
        }
    }
}