#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
const int N = 1e5 + 5;
int medians[N];
int tab[2 * N];
bool used[2 * N];
int getNext(int x, int del){
while(used[x]){
x += del;
}
return x;
}
int main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
int n, l, r;
cin >> n;
l = 1;
r = 2 * n - 1;
for(int i = 1 ; i <= n ; i++){
cin >> medians[i];
}
tab[1] = medians[1];
used[medians[1]] = 1;
for(int i = 2 ; i <= n ; i++){
l = getNext(l, 1);
r = getNext(r, -1);
if(medians[i] == medians[i - 1]){
tab[2 * i - 2] = l;
tab[2 * i - 1] = r;
used[l] = 1;
used[r] = 1;
}else if(medians[i - 1] < medians[i]){
if(!used[medians[i]]){
tab[2 * i - 2] = medians[i];
used[medians[i]] = 1;
}else{
tab[2 * i - 2] = r;
used[r] = 1;
r = getNext(r, -1);
}
tab[2 * i - 1] = r;
used[r] = 1;
}else{
if(!used[medians[i]]){
tab[2 * i - 2] = medians[i];
used[medians[i]] = 1;
}else{
tab[2 * i - 2] = l;
used[l] = 1;
l = getNext(l, 1);
}
tab[2 * i - 1] = l;
used[l] = 1;
}
}
for(int i = 1 ; i < 2 * n ; i++){
cout << tab[i] << " ";
}
cout << '\n';
}
