#include <iostream>
using namespace std;

int barrel[1001];

int main() {
	int n, num, cnt;
	scanf("%d", &n);
	
	
	for (int i = 0; i < n; i++) {
		scanf("%d", &num);
		if (barrel[num] == 0) cnt++;	// 统计总个数 
		barrel[num] = 1; 				// 每个学号计一次 
	} 
	
	printf("%d\n", cnt); 
	
	for (int i = 1; i <= 1000; i++) {
		if (barrel[i] == 1) printf("%d ", i);
	}
	
	cout<<endl;		/*这步是真的坑，我服了*/
    
    return 0;
}