#include using namespace std;

int a[10005]; int box[10005]; int main() { int n; cin >> n; for(int i = 1;i <= n;i++) { int score; cin >> score; box[score]++; } int cur = 0; for(int i = 1;i <= 10000;i++) { if(box[i] > 0) { cur++; a[cur] = i; } } cout << cur << endl; for(int i = 1;i <= cur;i++) { cout<< a[i] << " "; } return 0; }