#include <bits/stdc++.h>
using namespace std;
int n,a[100001],h,ans = 1;
bool istrue = false;
bool flag;
struct node
{
	int a;
	int b;
}c[100001];
bool cmp(node x,node y)
{
	return x.b > y.b;
}
inline int read()
{
	int f = 1,x = 0;
	char s = getchar();
	while (s < '0' || s > '9')
	{
		if (s == '-')
		{
			f = -f;
		}
		s = getchar();
	}
	while (s >= '0' && s <= '9')
	{
		x = x * 10 + s - '0';
		s = getchar();
	}
	return x * f;
}
int main()
{
	n = read();
	for (register int i = 1 ; i <= n ; i++)
	{
		a[i] = read();
	}
	sort(a + 1,a + 1 + n);
	h = a[1];
	c[ans].a = h;
	c[ans].b += 1;
	for (register int i = 2 ; i <= n ; i++)
	{
		if (a[i] == h)
		{
			c[ans].b += 1;
		}
		else
		{
			h = a[i];
			c[++ans].a = h;
			c[ans].b += 1;
		}
	}
	sort(c + 1,c + 1 + ans,cmp);
    if (ans % 2 == 1)
    {
       cout << -1;
       return 0;
    }
	for (register int i = 2 ; i <= ans ; i += 2)
    {
        if (c[i].b != c[i - 1].b)
        {
            istrue = true;
            break;
        }
    }
    if (istrue == true)
    {
        cout << -1;
        return 0;
    }
    for (register int i = 2 ; i < ans ; i += 2)
    {
        for (register int s = 1 ; s <= c[i].b ; s++)
        {
            cout << c[i].a << " " << c[i - 1].a << " ";
        }
    }
    for (register int i = 1 ; i < c[ans].b ; i++)
    {
        cout << c[ans].a << " " << c[ans - 1].a << " ";
    }
    cout << c[ans].a << " " << c[ans - 1].a;
	return 0;
}