#include <iostream>
#include <cmath>
#include <algorithm>
#include <queue>
using namespace std;
int n, a[10000006];
priority_queue <int, vector<int>, greater<int>> q;
void shu_ru() {
	cin >> n;
	for (int i = 1; i <= n; ++i) {
		int a;
		cin >> a;
		q.push(a);
	}
	for (int i = 1; i <= n; ++i) {
		a[i] = q.top();
		q.pop();
	}
}

void ji_suan() {
	for (int i = 1; i <= n; ++i) {
		for (int j = 1; j <= i;) {
			if (a[j] == a[j + 1]) {
				a[j] = 0;
				a[j + 1] = 0;
			}
			else if (a[j] == 0 || a[j + 1] == 0) {
				j += 2;
				continue;
			}
			j++;
		}
	}
}
void shu_chu() {
	for (int i = 1; i <= n; ++i) {
		if (a[i]) {
			cout << a[i] << endl;
		}
	}
}

int main() {
	shu_ru();
	ji_suan();
	shu_chu();
}