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;
        }

        int[] arr = new int[n];
        boolean hasNegative = false;

        // Take elements from user into array
        for (int i = 0; i < n; i++) {
            arr[i] = sc.nextInt();
            if (arr[i] < 0) {
                hasNegative = true;
            }
        }

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

        // Sort the array
        Arrays.sort(arr);

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

        // Find duplicates by comparing adjacent elements
        for (int i = 0; i < n - 1; i++) {
            if (arr[i] == arr[i + 1]) {
                // add only once
                if (!duplicates.contains(arr[i])) {
                    duplicates.add(arr[i]);
                }
            }
        }

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