#include <bits/stdc++.h>
using namespace std;
#define int long long
vector<int>A;
int lastMn, lastMx;
int mn(int m, vector<bool> &visited){
for(int i = lastMn; i <= m; i++){
if(!visited[i]){
return i;
}
}
return m+1;
}
int mx(int m, vector<bool> &visited){
for(int i = lastMx; i >= 1; i--){
if(!visited[i]){
return i;
}
}
return 0;
}
int32_t main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
// freopen("medians.in", "r", stdin);
//freopen("medians.out", "w", stdout);
int n;
cin>>n;
vector<int> a(n+2);
vector<bool>check(2*n+1);
for(int i=1; i<=n; i++)cin>>a[i];
A.push_back(a[1]);
check[a[1]]=true;
lastMx=2*n-1;
lastMn=1;
int l=mn(2*n-1, check), r=mx(2*n-1, check);
for(int i=2; i<=n; i++){
if(a[i-1]==a[i]){
l=mn(2*n-1, check);
A.push_back(l);
check[l]=true;
r=mx(2*n-1, check);
A.push_back(r);
check[r]=true;
}else if(a[i-1]>a[i]){
l=mn(2*n-1, check);
A.push_back(l);
check[l]=true;
if(check[a[i]]){
l=mn(2*n-1, check);
A.push_back(l);
check[l]=true;
}else{
A.push_back(a[i]);
check[a[i]]=true;
}
}else{
if(check[a[i]]){
r=mx(2*n-1, check);
A.push_back(r);
check[r]=true;
r=mx(2*n-1, check);
A.push_back(r);
check[r]=true;
}else{
A.push_back(a[i]);
check[a[i]]=true;
r=mx(2*n-1, check);
A.push_back(r);
check[r]=true;
}
}
}for(auto e: A){
cout<<e<<" ";
}cout<<endl;
return 0;
}
