#include <bits/stdc++.h>   using namespace std;   set<int> st;   set<int> en;   vector<int> out;   int main() {     ios_base::sync_with_stdio(0);     cin.tie(0);     int n;     cin >> n;     for (int i = 0; i < n; i++) {       int t;       cin >> t;       if (st.find(t) == st.end())         st.insert(t);       else if (en.find(t) == en.end())         en.insert(t);     }     int ma = 0;     for (set<int>::iterator it = st.begin(); it != st.end(); it++) {       out.push_back(*it);       ma = max(ma, (*it));     }     for (set<int>::reverse_iterator it = en.rbegin(); it != en.rend(); it++)       if ((*it) != ma) out.push_back(*it);     cout << out.size() << endl;     for (int i = 0; i < out.size(); i++) cout << out[i] <<    ;   }   