#include <bits/stdc++.h>
#define ll long long
const ll I = 2e5 + 9;
using namespace std;
set<int> smaller, bigger;
int BIT[I], ans[I], a[I], n, pos;
bool mark[I];
void update(int pos)
{
for (; pos <= 2 * n - 1; pos += pos & (-pos))
BIT[pos]++;
}
int get(int pos)
{
int rs = 0;
for (; pos > 0; pos -= pos & (-pos))
rs += BIT[pos];
return rs;
}
int main()
{
cin.tie(0)->sync_with_stdio(0);
cin >> n;
for (int i = 1; i <= n; i++)
cin >> a[i];
for (int i = 1; i <= 2 * n - 1; i++)
{
smaller.insert(i);
bigger.insert(i);
}
smaller.erase(a[1]);
bigger.erase(a[1]);
ans[1] = a[1];
mark[a[1]] = true;
update(a[1]);
pos = 1;
for (int i = 2; i <= n; i++)
{
int lf = get(a[i]), rt = i * 2 - 3 - lf;
// cout << lf << " " << rt << " " << i << " \n";
if (mark[a[i]] == false)
{
pos++;
ans[pos] = a[i];
update(a[i]);
mark[a[i]] = true;
smaller.erase(a[i]);
bigger.erase(a[i]);
lf++;
}
while (lf < i)
{
auto id = smaller.begin();
pos++;
ans[pos] = *id;
mark[(*id)] = true;
update((*id));
smaller.erase(*id);
bigger.erase(*id);
lf++;
}
while (rt < i - 1)
{
auto id = bigger.lower_bound(a[i]);
pos++;
ans[pos] = *id;
mark[(*id)] = true;
update((*id));
smaller.erase(*id);
bigger.erase(*id);
rt++;
}
}
for (int i = 1; i <= 2 * n - 1; i++)
cout << ans[i] << " ";
return 0;
}
