/*input
5
1 3 3 4 5
*/
#pragma GCC optimize ("O3")
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
int main()
{
ios_base::sync_with_stdio(false);
int n;
cin >> n;
int m[n];
for (int i = 0; i < n; i++)
cin >> m[i];
set<int>nebus;
for (int i = 1; i <= 2 * n - 1; i++)
nebus.insert(i);
for (int i = 0; i < n; i++)
nebus.erase(m[i]);
deque<int>answer;
int p[2 * n];
fill_n(p, 2 * n, n + 10);
for (int i = 0; i < n; i++)
p[m[i]] = min(p[m[i]], i);
for (int i = n - 1; i > 0; i--)
{
if (p[m[i]] == i)
nebus.insert(m[i]);
if (m[i] == m[i - 1])
{
auto it = nebus.lower_bound(m[i]);
assert(it != nebus.end());
answer.push_front(*it);
nebus.erase(it);
it = nebus.upper_bound(m[i]);
assert(it != nebus.begin());
it--;
answer.push_front(*it);
nebus.erase(it);
}
else
{
if (m[i] > m[i - 1])
{
auto it = nebus.lower_bound(m[i]);
assert(it != nebus.end());
answer.push_front(*it);
nebus.erase(it);
it = nebus.lower_bound(m[i]);
assert(it != nebus.end());
answer.push_front(*it);
nebus.erase(it);
}
else
{
auto it = nebus.upper_bound(m[i]);
assert(it != nebus.begin());
it--;
answer.push_front(*it);
nebus.erase(it);
it = nebus.upper_bound(m[i]);
assert(it != nebus.begin());
it--;
answer.push_front(*it);
nebus.erase(it);
}
}
}
nebus.insert(m[0]);
assert(nebus.size() == 1);
answer.push_front(*nebus.begin());
for (int i : answer)
cout << i << " ";
}
