#include <iostream>
#include <vector>
#include <deque>
#include <algorithm>
#include <set>

using namespace std;

int getUnusedMin(int min, set <int>& already_used) {
    while (already_used.find(min) != already_used.end()) {
        min++;
    }
    return min;
}

int getUnusedMax(int max, set <int>& already_used) {
    while (already_used.find(max) != already_used.end()) {
        max--;
    }
    return max;
}

int main() {
    int n;
    cin >> n;

    vector <int> v(n);
    for (auto& elem : v) {
        cin >> elem;
    }

    int min = 1;
    int max = INT_MAX;
    set <int> alredy_used;

    vector<int> result;
    result.push_back(v[0]);
    alredy_used.insert(v[0]);

    for (int i = 1; i < v.size(); ++i) {
        min = getUnusedMin(min, alredy_used);
        max = getUnusedMax(max, alredy_used);

        if (v[i - 1] == v[i]) {
            result.push_back(min);
            result.push_back(max);
            alredy_used.insert(min);
            alredy_used.insert(max);
            continue;
        }

        if (v[i - 1] < v[i]) {
            result.push_back((alredy_used.find(v[i]) != alredy_used.end() ? max : v[i]));
            alredy_used.insert((alredy_used.find(v[i]) != alredy_used.end() ? max : v[i]));

            max = getUnusedMax(max, alredy_used);
            result.push_back(max);
            alredy_used.insert(max);
            continue;
        }

        result.push_back((alredy_used.find(v[i]) != alredy_used.end() ? min : v[i]));
        alredy_used.insert((alredy_used.find(v[i]) != alredy_used.end() ? min : v[i]));

        min = getUnusedMin(min, alredy_used);
        result.push_back(min);
        alredy_used.insert(min);
    }

    for (auto& elem : result) {
        cout << elem << " ";
    }

    return 0;
}