#include <bits/stdc++.h> //Andrei Alexandru a.k.a Sho10
#define ll long long
#define double long double
#pragma GCC optimize("O3")
#pragma GCC optimize("Ofast")
#define all(a) (a).begin(), (a).end()
#define f first
#define s second
#define pb push_back
#define mp make_pair
#define pi pair
#define rc(s) return cout<<s,0
#define endl '\n'
#define mod 1000007
#define PI 3.14159265359
#define MAXN 100005
#define INF 1000000005
#define LINF 1000000000000000005ll
#define CODE_START ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
using namespace std;
int n,b[1000005],ans[2000005],l,r;
map<int,int>viz;
void mn(int pos){
while(viz[l]){
l++;
}
ans[pos]=l;
viz[l]=1;
}
void mx(int pos){
while(viz[r]){
r--;
}
ans[pos]=r;
viz[r]=1;
}
int32_t main(){
CODE_START
cin>>n;
for(int i=1;i<=n;i++)
{
cin>>b[i];
}
ans[1]=b[1];
viz[b[1]]=1;
l=1,r=2*n-1;
for(int i=2;i<=n;i++)
{
if(b[i]==b[i-1]){
mn(2*i-2);
mx(2*i-1);
}else if(b[i]>b[i-1]){
if(viz[b[i]]==0){
ans[2*i-2]=b[i];
viz[b[i]]=1;
mx(2*i-1);
}else {
mx(2*i-2);
mx(2*i-1);
}
}else {
if(viz[b[i]]==0){
ans[2*i-2]=b[i];
viz[b[i]]=1;
mn(2*i-1);
}else {
mn(2*i-2);
mn(2*i-1);
}
}
}
for(int i=1;i<=2*n-1;i++)
{
cout<<ans[i]<<' ';
}
cout<<endl;
}
