#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef pair<int, int> pii;
typedef long double ld;
#define F0R(i, a) for(int i=0; i<a; i++)
#define FOR(i, a, b) for(int i=a; i<=b; i++)
#define RFOR(i, b, a) for(int i=b; i>=a; i--)
#define f first
#define s second
#define pb push_back
#define INF 0x3f3f3f3f
#define MOD 998244353LL
#define MN 200005
int n;
int b[MN];
vi a;
bool used[MN];
int main(){
cin >> n;
FOR(i, 1, n){
cin >> b[i];
}
used[b[1]] = true;
a.pb(b[1]);
int l=1, r=2*n-1;
FOR(i, 2, n){
if(b[i] == b[i-1]){
while(used[l]) ++l;
while(used[r]) --r;
a.pb(l);
a.pb(r);
used[l] = used[r] = true;
} else if(b[i] < b[i-1]){
if(used[b[i]]){
while(used[l]) ++l;
a.pb(l); used[l] = true;
while(used[l]) ++l;
a.pb(l); used[l] = true;
} else{
a.pb(b[i]);
used[b[i]] = true;
while(used[l]) ++l;
a.pb(l); used[l] = true;
}
} else{
if(used[b[i]]){
while(used[r]) --r;
a.pb(r); used[r] = true;
while(used[r]) --r;
a.pb(r); used[r] = true;
} else{
a.pb(b[i]);
used[b[i]] = true;
while(used[r]) --r;
a.pb(r); used[r] = true;
}
}
}
for(auto u : a) cout << u << " ";
cout << "\n";
return 0;
}
