#include <bits/stdc++.h>

using namespace std;

int main() {
    setbuf(stdout, NULL);
    set<int> s;
    int n;
    cin >> n;
    int val;
    for (int i = 0; i < n; ++i) {
        cin >> val;
        s.insert(val);
    }
    cout << s.size() << endl;
    for (auto item: s) {
        cout << item << " ";
    }
    return 0;
}

直接STL解决一切问题？