#include<bits/stdc++.h>
using namespace std;

int main()
{
	int n;
	cin >> n;
	int a[101] = { 9999 };
	for (int i = 0; i < n; i++) {
		cin >> a[i];
	}
	sort(a, a + n);
	for (int i = n; i < n; i++) {
		if (a[i] == a[i + 1]) {
			a[i] = 9999;
		}
	}
	int k;
	sort(a, a + n);
	for (k = 0; true; k++) {
		if (a[k] == 9999) {
			break;
		}
	}
	cout << k << endl;
	for (int i = 0; i < k; i++) {
		cout << a[i] << " ";
	}
}