#include<bits/stdc++.h>
#define N 10000
using namespace std;
int main(){
	int a[N] = {0}, n, v, count;
	cin>>n;
	for(int i = 0; i < n; i++){
		cin>>v;
		a[v]++;x
	}
	for(int i = 0; i < N; i++){
		if(a[i] > 0){
			count++;
		}
	}
	cout<<count<<endl;
	for(int i = 0; i < N; i++){
		if(a[i] > 0){
			cout<<i<<" ";
		}
	}
}