This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
int n, b[100100];
set<int> q;
int main(){
    ios_base::sync_with_stdio(0);cin.tie(0);
    cin >> n;
    for (int i = 1; i <= 2*n-1; i++)
        q.insert(i);
    vector <int> ans;
    for (int i = 1; i <= n; i++){
        cin >> b[i];
        if (i == 1){
            q.erase(b[i]);
            ans.push_back(b[i]);
            continue;
        }
        if (b[i] == b[i-1]){
            ans.push_back(*q.begin());
            q.erase(q.begin());
            ans.push_back(*prev(q.end()));
            q.erase(prev(q.end()));
        }
        else if (b[i] < b[i-1]){
            if (q.find(b[i]) != q.end()){
                ans.push_back(b[i]);
                q.erase(b[i]);
                ans.push_back(*q.begin());
                q.erase(q.begin());
            } else {
                ans.push_back(*q.begin());
                q.erase(q.begin());
                ans.push_back(*q.begin());
                q.erase(q.begin());
            }
        }
        else {
            if (q.find(b[i]) != q.end()){
                ans.push_back(b[i]);
                q.erase(b[i]);
                ans.push_back(*prev(q.end()));
                q.erase(prev(q.end()));
            } else {
                ans.push_back(*prev(q.end()));
                q.erase(prev(q.end()));
                ans.push_back(*prev(q.end()));
                q.erase(prev(q.end()));
            }
        }
    }
    for (int i : ans)
        cout << i << ' ';
}
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