#include <bits/stdc++.h>

using namespace std;

int main()
{
  int n, m;

  cin>> n >> m;

  bool used[100001] = {false};
  int rem[100000];
  
  for (int i = 0; i < m; i++) {
    cin >> rem[i];
    used[rem[i]] = true;
  }

  int ui = 1;
  for (int i = 0; i < m; i++) {
    while (ui <= n) {
      if (used[ui]) {
	ui++;
      } else if (ui < rem[i]) {
	cout << ui++ << endl;
      } else {
	break;
      }
    }

    cout << rem[i] << endl;
  }
  for ( ; ui <= n; ui++) {
    if (!used[ui]) {
      cout << ui << endl;
    }
  }

  
  return 0;
}