#include <bits/stdc++.h>
using namespace std;
#define erorp(x) cout<<#x<<"={"<<(x.F)<<" , "<<x.S<<"}"<<endl
#define print(v,r) f(i,0,r) cout<<v[i]<<" "; cout<<endl
#define eror(x) cout<<#x<<'='<<(x)<<endl
#define f_(i,a,b) for(int i=a;i>=b;i--)
#define f(i,a,b) for(int i=a;i<b;i++)
#define nb(x) __builtin_popcount(x)
#define Add(x,y) x=(x+y)%mod;
#define maxm(a,b) a=max(a,b)
#define minm(a,b) a=min(a,b)
#define lst(x) x[x.size()-1]
#define sz(x) int(x.size())
#define mp make_pair
#define ll long long
#define pb push_back
#define S second
#define F first
const int N=1e6+99;
int n,t,a[N],Mn[N],Mx[N],mark[N];
vector<int> ans;
set<int> s;
int prv(int x){
int res=*prev(s.upper_bound(x));
s.erase(res);
return res;
}
int next(int x){
int res=*s.lower_bound(x);
s.erase(res);
return res;
}
int main(){
ios:: sync_with_stdio(0), cin.tie(0), cout.tie(0);
cin>>n;
f(i,1,n+1){ cin>>a[i]; mark[a[i]]++; }
f(i,1,2*n){
if(!mark[i]){
s.insert(i);
}
}
f_(i,n,2){
int u,v,mid=a[i],nmid=a[i-1];
if(--mark[a[i]]==0) s.insert(a[i]);
if(nmid==mid){
u=prv(mid),v=next(mid);
}
if(nmid<mid){
u=next(mid);
v=next(u);
}
if(mid<nmid){
u=prv(mid);
v=prv(u);
}
ans.pb(u);
ans.pb(v);
}
cout<<a[1]<<" ";
f_(i,ans.size()-1,0){
cout<<ans[i]<<" ";
}
}
