#include <iostream>
#include <algorithm>
using namespace std;
int a[1001] = {};
int main(){
int n,m,num = 0;
cin>>n;
for(int i = 0;i < n;i++){
cin>>m;
a[m] += 1;
}
for(int i = 0;i < 1001;i++){
if(a[i] != 0){
num++;
}
}
cout<<num<<endl;
for(int i = 0;i < 1001;i++){
if(a[i] != 0){
cout<<i<<" ";
}
}
return 0;
}/*10
20 40 32 67 40 20 89 300 400 15*/