#include <bits/stdc++.h>
#define _CRT_SECURE_NO_WARNINGS
using namespace std;
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define uniq(x) x.resize(unique(all(x)) - x.begin());
#define sort_uniq(x) sort(all(x)), uniq(x);
#define ll long long
#define ld long double
#define pii pair<int, int>
#define pll pair<ll, ll>
#define V vector
#define V2dll V<V<ll>>
#define V2dint V<V<int>>
#define V2dchar V<V<char>>
#define V2dbool V<V<bool>>
#define V3dll V<V<V<ll>>>
#define V3dint V<V<V<int>>>
#define V3dchar V<V<V<char>>>
#define lb lower_bound
#define ub upper_bound
#define pb push_back
#define eb emplace_back
#define FASTIO ios_base::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr);
#define INF INT32_MAX
#define blt __builtin_popcount
#define clr(x) x.clear()
#define ff first
#define ss second
#define popf pop_front
#define popb pop_back
#define sz(x) int(x.size())
#define rep(a, b, c, d) for (int a = b; a <= c; a += d)
#define repl(a, b, c, d) for (int a = b; a >= c; a -= d)
mt19937_64 rng(chrono::steady_clock().now().time_since_epoch().count());
int main()
{
FASTIO
int n;
cin >> n;
V<int> a(n + 1);
rep(i, 1, n, 1) cin >> a[i];
V<bool> used(2 * n + 1, false);
V<int> ans(2 * n + 1);
int l = 1, r = 2 * n - 1;
function<int(int,int)> adjust = [&](int pos, int dir) -> int {
for (int i = pos; i >= 1 && i <= 2 * n - 1; i += dir)
if (!used[i]) return i;
return -1;
};
function<void(int)> ml = [&](int pos) -> void {
ans[pos] = l;
used[l] = true;
l = adjust(l, 1);
};
function<void(int)> mr = [&](int pos) -> void {
ans[pos] = r;
used[r] = true;
r = adjust(r, -1);
};
ans[1] = a[1];
used[a[1]] = true;
if (a[1] == l) l = adjust(l, 1);
if (a[1] == r) r = adjust(r, -1);
rep(i, 2, n, 1) {
if (a[i] == a[i - 1]) {
ml(2 * i - 2);
mr(2 * i - 1);
continue;
}
if (a[i] > a[i - 1]) {
if (used[a[i]]) mr(2 * i - 2);
else {
ans[2 * i - 2] = a[i];
used[a[i]] = true;
if (a[i] == l) l = adjust(l, 1);
if (a[i] == r) r = adjust(r, -1);
}
mr(2 * i - 1);
}
else {
if (used[a[i]]) ml(2 * i - 2);
else {
ans[2 * i - 2] = a[i];
used[a[i]] = true;
if (a[i] == l) l = adjust(l, 1);
if (a[i] == r) r = adjust(r, -1);
}
ml(2 * i - 1);
}
}
rep(i, 1, 2 * n - 1, 1)
cout << ans[i] << " ";
}
