#include<bits/stdc++.h>
using namespace std;
using ll = long long;
const ll N = 2e5 + 2;
ll used[N] = {0};
multiset < ll > S;
void remove_max() {
auto R = S.end();
R --;
S.erase(R);
return ;
}
ll find_max() {
auto R = S.end();
R --;
used[*R] = 1;
return (*R);
}
void remove_min() {
auto R = S.begin();
S.erase(R);
return ;
}
ll find_min() {
auto R = S.begin();
used[*R] = 1;
return (*R);
}
int main() {
ll n, m, r, x,s, y, i, j,ind, t;
cin >> n;
ll a[n + 2];
for (i = 1; i <= n; i ++) {
cin >> a[i];
}
for (i = 1; i <= 2 * n - 1; i ++) S.insert(i);
vector < ll > ans;
ans.push_back(a[1]);
used[a[1]]= 1;
S.erase(S.find(a[1]));
for (i = 2; i <= n; i ++) {
if ( a[i] == a[i - 1]) {
ans.push_back(find_max());
ans.push_back(find_min());
remove_max();
remove_min();
}
else {
if ( a[i] < a[i- 1]) {
if ( used[a[i]] == 1) {
ans.push_back(find_min());
remove_min();
ans.push_back(find_min());
remove_min();
}
else {
ans.push_back(a[i]);
S.erase(S.find(a[i]));
ans.push_back(find_min());
remove_min();
}
}
else {
if ( used[a[i]] == 1) {
ans.push_back(find_max());
remove_max();
ans.push_back(find_max());
remove_max();
}
else {
ans.push_back(a[i]);
S.erase(S.find(a[i]));
ans.push_back(find_max());
remove_max();
}
}
}
// cout << i << "HI"<< endl;
used[a[i]] = 1;
}
for ( ll X : ans) cout <<X << " ";
}
