// #pragma GCC optimize("Ofast,no-stack-protector,unroll-loops,fast-math")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,sse4.1,sse4.2,popcnt,abm,mmx,avx")
// #pragma comment(linker, "/stack:200000000"]

#include <iostream>
#include <vector>
#include <cmath>
#include <algorithm>
#include <unordered_set>
#include <unordered_map>
#include <set>
#include <map>
#include <queue>
#include <deque>
#include <bitset>
#include <stack>
#include <random>
#include <fstream>
#include <sstream>
#include <chrono>

#define fi first
#define se second
#define pb push_back
#define ll long long
#define ld long double
#define hm unordered_map
#define pii pair<int, int>
#define sz(a) (int)a.size()
#define all(a) a.begin(), a.end()
#define cinv(v) for (auto& x: v) cin >> x
#define fr(i, n) for (int i = 0; i < n; ++i)
#define fl(i, l, n) for (int i = l; i < n; ++i)

#define int ll

template <typename T1, typename T2> inline bool chkmin(T1 &x, const T2 &y) {if (x > y) {x = y; return 1;} return 0;}
template <typename T1, typename T2> inline bool chkmax(T1 &x, const T2 &y) {if (x < y) {x = y; return 1;} return 0;}

using namespace std;

#ifdef LOCAL
	#define dbg(x) cerr << #x << " : " << x << '\n'
	const int maxn = 20;
#else
	#define dbg(x)
	const int maxn = 500 + 20;
#endif

//tg: @galebickosikasa

ostream& operator << (ostream& out, const pii& v) {
	out << v.fi << ", " << v.se;
	return out;
}

template<typename T> ostream& operator << (ostream& out, const vector<T>& v) {
    for (auto& x: v) out << x << " ";
    return out;
}

istream& operator >> (istream& in, pii& a) {
	in >> a.fi >> a.se;
	return in;
}

const ll inf = (ll) 2e9;
const ld pi = asin (1) * 2;
const ld eps = 1e-8;
const ll mod = (ll)1e9 + 7;
const ll ns = 97;

mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());

struct tree {
	vector<int> a, b, c; // unused_high, unused_low, res
	int size = 0, capacity;

	tree (int n) {
		while ((1<<size) < n) ++size;
		++size;
		size = (1<<size);
		capacity = (size>>1);
		a = b = c = vector<int> (size);
	}

	inline void render (int i) {
		i >>= 1;
		while (i) {
			int t = min (a[i * 2 + 1], b[i * 2]);
			a[i] = a[i * 2] + a[i * 2 + 1] - t;
			b[i] = b[i * 2] + b[i * 2 + 1] - t;
			res[i] = res[i * 2] + res[i * 2 + 1] + t;
			i >>= 1;
		}
	}

	inline void add (int x, int y) {
		x += capacity, y += capacity;
		++b[y];
		++a[x];
		render (x);
		render (y);
	}




signed main () {
	ios_base::sync_with_stdio(false);
	cin.tie(nullptr);
	cout.tie(nullptr);
#ifndef LOCAL
	freopen ("cardgame.in", "r", stdin);
	freopen ("cardgame.out", "w", stdout);
#endif

	int n;
	cin >> n;
	vector<int> used (2 * n);
	vector<int> a (n);
	cinv (a);
	for (auto& x: a) --x;
	for (auto& x: a) used[x] = 1;
	vector<int> b;
	fr (i, n) if (!used[i]) b.pb (i);






}