#include <iostream>
#include <cstring>
using namespace std;
int main()
{
    int n,a[1009]={0},t,s=0;
    cin>>n;
    for (int i=1;i<=n;++i)
    {
        cin>>t;
        a[t]++;
    }
    for (int i=1;i<=1000;++i)
    {
        if (a[i]!=0)++s;
    }
    cout<<s<<endl;
    for (int i=1;i<=1000;++i)
    {
        if (a[i]!=0)cout<<i<<" ";
    }
    cout<<endl;
    return 0;
}