#include <bits/stdc++.h>
using namespace std;
const int M = 2e5 + 5;
int f[M];
vector<int> v, ant;
set<int> s;
int n, m;
int main() {
#ifdef HOME
freopen("medians.in", "r", stdin);
freopen("medians.out", "w", stdout);
#endif
ios::sync_with_stdio(false);
cin.tie(0), cout.tie(0);
int lst;
cin >> n;
v.resize(n);
for (auto &i: v) {
cin >> i;
f[i]+= 1; }
m = 2 * n - 1;
for (int i = 1; i <= m; ++i)
if (!f[i])
s.insert(i);
lst = v.back();
if (!--f[lst])
s.insert(lst);
for (int i = n - 2; i >= 0; --i) {
if (v[i] == lst) {
auto l = prev(s.lower_bound(v[i]));
auto r = s.lower_bound(v[i]);
ant.push_back(*l), ant.push_back(*r);
s.erase(l);
s.erase(r); }
else if (v[i] > lst) {
auto l = prev(s.upper_bound(v[i]));
auto r = prev(l);
ant.push_back(*l), ant.push_back(*r);
s.erase(l);
s.erase(r); }
else {
auto l = s.lower_bound(v[i]);
auto r = next(l);
ant.push_back(*l), ant.push_back(*r);
s.erase(l);
s.erase(r); }
lst = v[i];
if (--f[v[i]] == 0)
s.insert(v[i]); }
ant.push_back(*begin(s));
reverse(begin(ant), end(ant));
for (auto i: ant)
cout << i << ' ';
cout << endl;
return 0; }
