import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();

        int sum = 0;
        for (int i = 0; i < n; i++) {
            int a = scanner.nextInt();
            sum = sum^a;
        }
        System.out.println(sum);
        scanner.close();
    }
}