import java.util.HashMap;

public class TabliceZadanie12 {

	public static int solution(int[] tab) {
		HashMap<Integer, Integer> mapa = new HashMap<Integer, Integer>();
		int result = 0;
		for (int i = 0; i < tab.length; i++) {
			if (mapa.containsKey(tab[i]))
				mapa.replace(tab[i], mapa.get(tab[i]) + 1);
			else
				mapa.put(tab[i], 1);
		}
		for (Integer klucz : mapa.keySet()) {
			Integer value = mapa.get(klucz);
			if (value == 1)
				result = klucz;
		}
		return result;
	}

	public static void main(String[] args) {
		int[] tablica = { 4, 3, 4, 8, 3, 5, 5 };
		System.out.println(solution(tablica));
	}
}