#include <bits/stdc++.h>
#define ll long long
using namespace std;
const int INF = 1e9;
const int MOD = 1e9 + 7;
int n, a[100002], b[200002], viz[200002];
set<int>s;
int main ()
{
ios_base::sync_with_stdio(false);
cin.tie(0); cout.tie(0);
cin >> n;
for (int i = 1; i <= n; i++)
cin >> a[i];
viz[a[1]] = 1;
for (int i = 1; i < 2 * n; i++)
s.insert(i);
s.erase(a[1]);
for (int i = 2; i <= n; i++) {
if (a[i] == a[i - 1]) {
b[2 * i - 1] = *s.begin();
b[2 * i - 2] = *s.rbegin();
s.erase(b[2 * i - 1]);
s.erase(b[2 * i - 2]);
viz[b[2 * i - 2]] = 1;
viz[b[2 * i - 1]] = 1;
}
else if (a[i] > a[i - 1]) {
b[2 * i - 1] = *s.rbegin();
auto it = s.rbegin();
if (viz[a[i]]) {
it--;
b[2 * i - 2] = *it;
}
else
b[2 * i - 2] = a[i];
s.erase(b[2 * i - 1]);
s.erase(b[2 * i - 2]);
viz[b[2 * i - 2]] = 1;
viz[b[2 * i - 1]] = 1;
}
else {
b[2 * i - 1] = *s.begin();
auto it = s.begin();
if (viz[a[i]]) {
it++;
b[2 * i - 2] = *it;
}
else
b[2 * i - 2] = a[i];
s.erase(b[2 * i - 1]);
s.erase(b[2 * i - 2]);
viz[b[2 * i - 2]] = 1;
viz[b[2 * i - 1]] = 1;
}
assert(b[2 * i - 1] != b[2 * i - 2]);
}
b[1] = a[1];
for (int i = 1; i < 2 * n; i++)
cout << b[i] << " ";
return 0;
}
