import java.util.*;

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

        int n = sc.nextInt();

        // if n is negative → invalid
        if (n < 0) {
            System.out.println("Invalid input");
            return;
        }

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

        // read array elements
        for (int i = 0; i < n; i++) {
            arr[i] = sc.nextInt();
            if (arr[i] < 0) {
                invalid = true;
            }
        }

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

        boolean found = false;

        // check duplicates (simple nested loop)
        for (int i = 0; i < n; i++) {
            for (int j = i + 1; j < n; j++) {
                if (arr[i] == arr[j]) {
                    System.out.println(arr[i]);
                    found = true;
                    break; // print once per duplicate value
                }
            }
        }

        if (!found) {
            System.out.println("No duplicates found");
        }
    }
}