#include <iostream>
#include <fstream>
#include <vector>
#include <list>
#include <cmath>
#include <algorithm>

using namespace std;

int hashh(int N) {
	return N % 2671;
}

vector <list <int>> hashtable(2671);

int main() {
	ifstream f("input.txt");
	ofstream f1("output.txt");

	int a;
	f >> a;

	while (a != 0) {

		if (a > 0) {
			bool is_in = false;

			int h;
			h = hashh(a);

			for (auto iter = hashtable[h].begin(); iter != hashtable[h].end(); iter++) {
				if (*iter == a) {
					is_in = true;
					break;
				}
			}

			if (!is_in) {
				hashtable[hashh(a)].push_back(a);
			}
		}
		else {
			int h;
			h = hashh(abs(a));

			for (auto iter = hashtable[h].begin(); iter != hashtable[h].end(); iter++) {
				if (*iter == abs(a)) {
					hashtable[h].erase(iter);
					break;
				}
			}
		}
        f >> a;
	}

	vector <int> vec;

	for (int j = 0; j < hashtable.size(); j++) {
		for (auto iter = hashtable[j].begin(); iter != hashtable[j].end(); iter++) {
			vec.push_back(*iter);
		}
	}

	sort(vec.begin(), vec.end());

	for (auto iter = vec.begin(); iter != vec.end(); iter++) {
		f1 << *iter << ' ';
	}

	f.close();
	f1.close();

	return 0;
}