import java.util.Arrays;
import java.util.Scanner;

public class D {
    public static void main(String[] args) {
        int[] a = new int[cin.nextInt()];
        for (int i = 0; i < a.length; i++) {
            a[i] = cin.nextInt();
        }

        Arrays.sort(a);
        int count = 0;
        for (int i = 0; i < a.length; i++) {
            if (i == 0 || a[i] != a[i - 1])
                ++count;
        }
        System.out.println(count);


        for (int i = 0; i < a.length; i++) {
            if (i == 0 || a[i] != a[i - 1])
                System.out.print(a[i] + " ");
        }
        System.out.println();
    }

    static Scanner cin = new Scanner(System.in);
}