import java.util.Scanner;

public class Main {
	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		long[] a = new long[n];
		for (int i = 0; i < n; i++) {
			a[i] = sc.nextLong();
		}
		sc.close();

		long b = 0;
		for (int i = 0; i < n; i++) {
			b |= a[i];
		}

		for (int i = 0; i < 63; i++) {
			long x = 1L << i;
			if (x + b == (x ^ b)) {
				System.out.println(x);
				return;
			}
		}
	}
}