#include <iostream>
#include <map>

using namespace std;

const int N = 100010;

int n, m, maxn;
map<int, int> k;
bool vis[N];

int main() {
	cin >> n;
	for (int i = 1, x; i <= n; i ++ ) {
		cin >> x;
		m += (!k[x]);
		k[x] ++ ;
		maxn = max(maxn, x);
	}
	if (m & 1) {
		cout << -1 << endl;
		return 0;
	}
	for (auto& pair : k) {
		if (!vis[pair.first]) {
			bool b = true;
			int a1 = pair.first, a2 = pair.second;
			vis[a1] = true;
			for (auto& pairr : k) {
				int b1 = pairr.first, b2 = pairr.second;
				if (!vis[b1]) {
					if (a2 == b2) {
						for (int i = 1; i <= a2; i ++ )
							cout << a1 << " " << b1 << " ";
						vis[b1] = true, b = !b;
						break;
					} else if (a2 & 1 && b2 & 1) {
						cout << a1 << " " << b1 << " ";
						for (int i = 1; i < a2; i ++ )
							cout << a1 << " ";
						for (int i = 1; i < b2; i ++ )
							cout << b1 << " ";
						vis[b1] = true, b = !b;
                        break;
					}
				}
			}
			if (b) {
                cout << -1 << endl;
                return 0;
            }
		}
	}
	return 0;
}