#include <stdio.h>

int N, A[2020];

int main()
{
	scanf ("%d", &N);
	for (int i = 0; i < N; i++) scanf ("%d", &A[i]);

	int x = 0;
	for (int i = 0; i < N; i++) for (int j = i + 1; j < N; j++) if (x < (A[i] ^ A[j])) x = A[i] ^ A[j];

	printf ("%d\n", x);
	return 0;
}