#include "bits/stdc++.h"

using namespace std;

void solve() {
    int n;
    cin >> n;
    set<int> nums;
    for (int i = 1; i <= 2 * n; i++)
        nums.insert(i);
    for (int i = 1; i < n; i++) {
        int x;
        cin >> x;
        nums.erase(x);
        if (x % 2) {
            nums.erase(x + 1);
            cout << x + 1 << endl;
        } else {
            nums.erase(x - 2);
            cout << x - 2 << endl;
        }
    }
//    for (auto i: nums)cout << i << ' ';
}

string s;

int main() {
//    ios::sync_with_stdio(false);
//    cout.tie(nullptr);
//    cin.tie(nullptr);
    solve();
    exit(0);
    cin >> s >> t;
    int i = 0, current = 0, ans = (int) s.size();
    for (char c: t) {
        while (i < s.size() and s[i] > c) {
            ++current;
            ++i;
        }
        if (s[i] < c) {
            ans = min(ans, current);
            break;
        }
        ans = min(ans, current + (int) s.size() - i);
    }
    cout << ans << '\n';
    return 0;
}

answer.code: In function ‘int main()’:
answer.code:34:17: error: ‘t’ was not declared in this scope; did you mean ‘tm’?
   34 |     cin >> s >> t;
      |                 ^
      |                 tm