#include <bits/stdc++.h>
#define int long long
using namespace std;
int32_t main() {
ios_base::sync_with_stdio(0);
cin.tie(nullptr);
int n;
cin >> n;
vector<int> b(n);
for (int i = 0; i < n; ++i) {
cin >> b[i];
}
set<int> st;
for (int i = 1; i <= 2 * n - 1; ++i) {
st.insert(i);
}
vector<int> a;
a.push_back(b[0]);
st.erase(b[0]);
for (int i = 1; i < n; ++i) {
if (b[i - 1] == b[i]) {
a.push_back(*st.begin());
a.push_back(*st.rbegin());
st.erase(st.begin());
st.erase(*--st.end());
} else if (b[i - 1] < b[i]) {
if (st.count(b[i])) {
a.push_back(b[i]);
st.erase(b[i]);
a.push_back(*st.rbegin());
st.erase(*--st.end());
} else {
a.push_back(*st.begin());
st.erase(*st.begin());
a.push_back(*st.begin());
st.erase(*st.begin());
}
} else {
if (st.count(b[i])) {
a.push_back(b[i]);
st.erase(b[i]);
a.push_back(*st.begin());
st.erase(st.begin());
} else {
a.push_back(*st.rbegin());
st.erase(*--st.begin());
a.push_back(*st.rbegin());
st.erase(*--st.end());
}
}
}
for (auto& u: a) {
cout << u << " ";
}
return 0;
}
