#include <bits/stdc++.h> using namespace std; const int N = 1e5 + 10; int medians[N], tab[2 * N + 10], used[2 * N + 10], sign[2 * N + 10]; vector <int> UnUsed; priority_queue <pair<int, int>> Q; int main() { //-1 mniejsza, 0 rowna, +1 wieksza int n; cin >> n; for(int i = 1; i <= n; i++) { cin >> medians[i]; } tab[1] = medians[1]; used[tab[1]] = true; for(int i = 2; i <= n; i++) { if(medians[i] == medians[i - 1]) { sign[2 * i - 1] = -1; sign[2 * i - 2] = 1; } if(medians[i - 1] < medians[i]) { if(used[medians[i]]) { sign[2 * i - 1] = 1; sign[2 * i - 2] = 1; } else { sign[2 * i - 1] = 0; sign[2 * i - 2] = 1; } } if(medians[i - 1] > medians[i]) { if(used[medians[i]]) { sign[2 * i - 1] = -1; sign[2 * i - 2] = -1; } else { sign[2 * i - 1] = 0; sign[2 * i - 2] = -1; } } tab[2 * i - 1] = tab[2 * i - 2] = medians[i]; used[medians[i]] = true; } for(int i = 2 * n - 1; i >= 1; i--) { if(sign[i] == -1) Q.push({-tab[i], i}); if(sign[i] == 1) Q.push({tab[i], i}); if(!used[i]) UnUsed.push_back(i); } for(auto x : UnUsed) { tab[Q.top().second] = x; Q.pop(); } for(int i = 1; i <= 2 * n - 1; i++) { cout << tab[i] << ' '; } return 0; }