Codeforces

#include <iostream>
#include <map>

using namespace std;

int main()
{
    int n, k, cont = 0, contv = 0;

    cin >> n;

    map < int, int > mapa;

    for ( int i = 0 ; i < n ; i++)
    {
        cin >> k;

        mapa[k]++;
    }

    for ( auto i:mapa)
    {
        if( i.second)
            cont++;
    }

    cout << cont <<endl;

    for ( auto i:mapa)
    {
        cout << i.first << " ";
    }

    return 0;
}