#include<bits/stdc++.h>
using namespace std;
using ll = long long;
const ll N = 2e5 + 2;
set < ll > uragsh_ind[N], aragsh_ind[N];
ll uragsh[N], aragsh[N], a[N], b[N], used[N];
int main() {
ll n, m, r, x,s, y, i, j,ind, ans, t;
cin >> n;
for (i = 1; i <= n; i ++) {
cin >> a[i];
}
used[a[1]] = 1;
for (i = 1; i <= 2 * n - 1; i ++) b[i]= -1;
b[1] = a[1];
for (i = 2; i <= n; i ++) {
if ( a[i] == a[i - 1]) {
uragsh[a[i]] = aragsh[a[i]] = 1;
uragsh_ind[a[i]].insert(i);
aragsh_ind[a[i]].insert(i);
}
else {
if ( a[i] > a[i- 1]) {
aragsh_ind[a[i]].insert(i);
aragsh[a[i]] =1;
used[a[i]] = 1;
b[2 * i - 1] = a[i];
}
else {
uragsh_ind[a[i]].insert(i);
used[a[i]] = 1;
uragsh[a[i]] = 1;
b[2 * i - 1] = a[i];
}
}
}
queue < ll > q;
for (i =1 ; i <= 2 *n - 1; i ++) {
for ( ll ind : uragsh_ind[i]) {
s = q.front();
q.pop();
b[ind * 2 - 2] = s;
}
if ( uragsh_ind[i].empty() && aragsh_ind[i].empty())q.push(i);
}
stack < ll > v;
while(!q.empty()) {
v.push(q.front());
q.pop();
}
for (i = 2 * n - 1; i >= 1; i --) {
for ( ll ind : aragsh_ind[i]) {
s = v.top();
v.pop();
//ind =-ind;
if ( b[ind * 2 - 1] == -1) b[ind * 2 - 1] = s;
else b[ind * 2 - 2] = s;
}
}
// for (i = 1; i <= 2 * n - 1; i ++) {
// for (j = i + 1; j <= 2 * n - 1; j ++) {
// if ( b[i] == b[j]) {
// while(1);
// }
// }
// }
for (i = 1; i <= 2 *n - 1; i ++) {
if ( b[i] < 1 || b[i] > 2 * n - 1) {
while(1);
}
cout << i << " ";
}
cout <<"\n";
}
