import java.util.Scanner;

import java.util.TreeSet;

public class MissingGnomes {

public static void main(String[] args) {

Scanner sc = new Scanner(System.in);

String line = sc.nextLine();

int n = Integer.parseInt(line.substring(0, line.indexOf(" ")));

int m = Integer.parseInt(line.substring(line.indexOf(" ")+1));

TreeSet<Integer> set = new TreeSet<>();

int[] gnomes = new int[m];

// add all the gnomes

for (int i = 1; i <= n; i++) {

set.add(i);

}

int j = 0;

for (int i = 0; i < m; i++) {

int temp = sc.nextInt();

if(set.contains(temp)) set.remove(temp);

gnomes[j++] = temp;

}

gnomeOrder(set, gnomes);

}

public static void gnomeOrder(TreeSet<Integer> set, int[] gnomes) {

int i = 0; //incrementer of the array

while(i < gnomes.length && set.size() != 0){

if(gnomes[i] > set.first()){

System.out.println(set.pollFirst());

}

else{

System.out.println(gnomes[i++]);

}

}

while(i < gnomes.length){

System.out.println(gnomes[i++]);

}

while(set.size() != 0){

System.out.println(set.pollFirst());

}

}

}