#include <bits/stdc++.h>
using std::vector;
using std::array;
using std::pair;
using std::tuple;
void show(const vector<int>& v) {
const int n = v.size();
std::cout << n << '\n';
for (int i = 0; i < n; ++i) {
std::cout << v[i] << " \n"[i + 1 == n];
}
}
int main() {
std::ios_base::sync_with_stdio(false);
std::cin.tie(nullptr);
int N;
std::cin >> N;
vector<int> A(N);
for (auto& x : A) {
std::cin >> x;
}
const auto try_seq = [&](const int first, const int dif) {
std::multiset<int> set(A.begin(), A.end());
std::multiset<int> dist;
for (auto itr = set.begin(); std::next(itr) != set.end(); ++itr) {
dist.insert(*std::next(itr) - *itr);
}
int element = first;
vector<int> taken;
while (true) {
auto itr = set.find(element);
if (itr == set.end()) {
return;
}
if (itr != set.begin()) {
dist.erase(dist.find(*itr - *std::prev(itr)));
}
if (std::next(itr) != set.end()) {
dist.erase(dist.find(*std::next(itr) - *itr));
}
if (itr != set.begin() and std::next(itr) != set.end()) {
dist.insert(*std::next(itr) - *std::prev(itr));
}
taken.push_back(element);
set.erase(itr);
if (*dist.begin() == *dist.rbegin()) {
show(taken);
show(vector<int>(set.begin(), set.end()));
std::exit(EXIT_SUCCESS);
}
element += dif;
}
};
std::sort(A.begin(), A.end());
try_seq(A[0], A[1] - A[0]);
try_seq(A[0], A[2] - A[0]);
try_seq(A[1], A[2] - A[1]);
std::cout << -1 << '\n';
return 0;
}
