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

int main() {
    int n;
    std::cin >> n;
    std::vector<int> cards(n);
    for (int i = 0; i < n; ++i) {
        std::cin >> cards[i];
    }

    std::set<int> sums;
    for (int i = 0; i < n; ++i) {
        for (int j = i + 1; j < n; ++j) {
            sums.insert(cards[i] + cards[j]);
        }
    }

    std::vector<int> uniqueSums(sums.begin(), sums.end());

    std::cout << uniqueSums.size() << std::endl;
    for (int i = 0; i < uniqueSums.size(); ++i) {
        if (i > 0) {
            std::cout << " ";
        }
        std::cout << uniqueSums[i];
    }
    std::cout << std::endl;

    return 0;
}
/**************************************************************
	Problem: 1334
	User: panyuchen
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2076 kb
****************************************************************/