#include <bits/stdc++.h>

using namespace std;

#define int long long
#define fir first
#define sec second
#define mkp make_pair 
#define pb push_back
#define lep( i, l, r ) for ( int i = ( l ); i <= ( r ); ++ i )
#define rep( i, r, l ) for ( int i = ( r ); i >= ( l ); -- i )

typedef long long ll;
typedef long double ld;
typedef pair < int, int > pii;

char _c; bool _f; template < class type > inline void read ( type &x ) {
	_f = 0, x = 0;
	while ( _c = getchar (), !isdigit ( _c ) ) if ( _c == '-' ) _f = 1;
	while ( isdigit ( _c ) ) x = x * 10 + _c - '0', _c = getchar (); if ( _f ) { x = -x; }
}

template < class type > inline void chkmin ( type &x, type y ) { x = ( x <= y ? x : y ); }
template < class type > inline void chkmax ( type &x, type y ) { x = ( x >= y ? x : y ); }

const int N = 1e5 + 5;

int n, m;
int a[N], tong[N];
queue < int > q1, q2;

void Solve () {
  cin >> m >> n;
  for ( int i = 1; i <= n; i ++ ) {
    cin >> a[i];
    tong[a[i]] = 1;
    q1.push ( a[i] );
  }
  for ( int i = 1; i <= m; i ++ ) {
    if ( !tong[i] ) {
      q2.push ( i );
    }
  }
  for ( int i = 1; i <= m; i ++ ) {
    if ( !q1.size () ) {
      cout << q2.front () << " ";
      q2.pop ();
    }
    else if ( !q2.size () ) {
      cout << q1.front () << " ";
      q1.pop ();
    }
    else {
      if ( q1.front () < q2.front () ) {
        cout << q1.front () << " ";
        q1.pop ();
      }
      else {
        cout << q2.front () << " ";
        q2.pop ();
      }
    }
  }
}

signed main () {
#ifdef judge
  freopen ( "Code.in", "r", stdin );
  freopen ( "Code.out", "w", stdout );
  freopen ( "Code.err", "w", stderr );
#endif
  Solve ();
  return 0;
}