#include <bits/stdc++.h>
using namespace std;
#define ll long long
ll t,n,a[200005],x;
set<ll>s;
set<ll>::iterator it;
int main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);cout.tie(0);
cin>>n;
for(int i=1;i<=n;i++)
cin>>a[i];
for(int i=1;i<=2*n-1;i++)
s.insert(i);
s.erase(a[1]);
x=a[1];
cout<<a[1]<<" ";
for(int i=2;i<=n;i++)
{
if(s.find(a[i])!=s.end())
{
s.erase(a[i]);
cout<<a[i]<<" ";
if(a[i]<x)it=s.begin();
else
{
it=s.end();
it--;
}
cout<<*it<<" ";
s.erase(it);
x=a[i];
}
else
{
if(a[i]<=x)it=s.begin();
else
{
it=s.end();
it--;
}
cout<<*it<<" ";
s.erase(it);
if(a[i]<x)it=s.begin();
else
{
it=s.end();
it--;
}
cout<<*it<<" ";
s.erase(it);
x=a[i];
}
}
return 0;
}
