import java.util.*;

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

        int n = scn.nextInt();
        int[] arr = new int[n];

        boolean invalid = false;
        for (int i = 0; i < n; i++) {
            arr[i] = sc.nextInt();
            if (arr[i] < 0) {
                invalid = true;
            }
        }

        if (invalid) {
            System.out.println("Invalid input");
            return;
        }

        Set<Integer> seen = new HashSet<>();
        Set<Integer> duplicates = new LinkedHashSet<>();

        for (int x : arr) {
            if (!seen.add(x)) {
                duplicates.add(x);
            }
        }

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