#include <bits/stdc++.h>

using namespace std;

//map排序(key)的比较器
struct cmpFunction {
    bool operator()(const int &k1, const int &k2) const {
        return k1 < k2;
    }
};

int main() {
    int n;
    cin >> n;
    map<int, int, cmpFunction> _map;
    for (int i = 0; i < n; ++i) {
        int c;
        cin >> c;
        _map[c]++;
    }
    //输出结果
    cout << _map.size() << endl;
    for (map<int, int>::iterator iter = _map.begin(); iter != _map.end(); ++iter) {
        cout << iter->first << " ";
    }

    return 0;
}