#include<iostream>
#include<map>
using namespace std;
map<int,int> hs;
int main(){
    int n;
    cin>>n;
    while(n--){
        int x;
        cin>>x;
        hs[x]++;
    }
    cout<<hs.size()<<endl;
    for(auto x:hs)
    cout<<x.first<<' ';
    return 0;
}