// Naive O(N^2) solution, which should be much too slow.

#include <iostream>
#include <vector>
#include <array>
#include <cassert>
#include <numeric>

using namespace std;

std::array<vector<int>, 2> pick_players(const std::array<vector<int>, 2>& choices) {
  vector<int> remaining_players;
  for (int i = 0; i < choices[0].size() * 2; ++i) {
    remaining_players.push_back(i + 1);
  }

  std::array<vector<int>, 2> teams;
  for (int i = 0; i < choices[0].size(); ++i) {
    for (int t = 0; t <= 1; ++t) {
      const int choice = choices[t][i];
      teams[t].push_back(remaining_players.at(choice));
      remaining_players.erase(remaining_players.begin() + choice);
    }
  }
  
  return teams;
}

int main() {
  int N;
  cin >> N;
  assert(N % 2 == 0);
  std::array<vector<int>, 2> choices;
  choices[0].reserve(N);
  choices[1].reserve(N);
  for (int i = 0 ; i < N; ++i) {
    int choice;
    cin >> choice;
    // In the problem statement, the indexes are 1-based.
    choices[i >= N/2].push_back(choice - 1);
  }
  auto teams = pick_players(choices);
  for (const auto& team: teams) {
    for (int player : team) {
      cout << player << " ";
    }
    cout << endl;
  }
}