#include <bits/stdc++.h>
#define lsb(x) (x & (-x))
#define ll long long
#define ull unsigned long long
// 217
// 44
using namespace std;
const int MAXN = (int) 1e5;
int arr[MAXN + 1], sol[2 * MAXN + 1];
bool vis[2 * MAXN + 1];
inline int get_max(int &b) {
while(vis[b]) {
b--;
}
vis[b] = 1;
return b;
}
inline int get_min(int &a) {
while(vis[a]) {
a++;
}
vis[a] = 1;
return a;
}
int main() {
//ifstream cin("A.in");
//ofstream cout("A.out");
int i, n;
ios::sync_with_stdio(false);
cin >> n;
for(i = 1; i <= n; i++) {
cin >> arr[i];
}
sol[1] = arr[1];
vis[arr[1]] = 1;
int a = 1, b = 2 * n - 1;
int p = 2;
for(i = 2; i <= n; i++) {
if(arr[i] == arr[i - 1]) {
sol[p] = get_max(b);
sol[p + 1] = get_min(a);
}
if(arr[i] > arr[i - 1]) {
if(vis[arr[i]] == 0) {
sol[p] = arr[i];
vis[arr[i]] = 1;
sol[p + 1] = get_max(b);
}
else {
sol[p] = get_max(b);
sol[p + 1] = get_max(b);
}
}
if(arr[i] < arr[i - 1]) {
if(vis[arr[i]] == 0) {
sol[p] = arr[i];
vis[arr[i]] = 1;
sol[p + 1] = get_min(a);
}
else {
sol[p] = get_min(a);
sol[p + 1] = get_min(a);
}
}
p += 2;
}
for(i = 1; i < 2 * n; i++) {
cout << sol[i] << " ";
}
//cin.close();
//cout.close();
return 0;
}
