#include "bits/stdc++.h"
#define rep(i, a, n) for (auto i = a; i <= (n); ++i)
#define revrep(i, a, n) for (auto i = n; i >= (a); --i)
#define all(a) a.begin(), a.end()
#define sz(a) (int)(a).size()

using namespace std;
using ll = long long;
using pii = pair<int, int>;
using vi = vector<int>;
using vvi = vector<vi>;


int main() {
	ios::sync_with_stdio(0); cin.tie(0);

	int n, m; cin >> n >> m;
	vi as(m); 
	vi mark(n);
	for (auto &x: as) {
		cin >> x;
		x--;
		mark[x] = 1;
	}
	vi bs;
	rep(i, 0, n - 1) if (mark[i] == 0) {
		bs.push_back(i);
	}
	auto it = as.begin();
	vi ans;
	for (auto x: bs) {
		while (it != as.end() && *it < x) {
			ans.push_back(*it);
			it++;
		}
		ans.push_back(x);
	}
	for (auto x: ans) printf("%d\n", x + 1);
	return 0;
}