#include <cstdio>

#define MAX_N 100005

int A[MAX_N];
int best;
int i, j, N;

int main ()
{
    freopen ("xormax.in", "r", stdin);
    freopen ("xormax.out", "w", stdout);
    
    scanf ("%d", &N);
    for (i = 1; i <= N; ++i) scanf ("%d", A + i);
    for (i = 1; i <= N; ++i)
        for (j = 1; j <= i - 1; ++j)
            if (A[i]^A[j] > best) best = A[i]^A[j];
    printf ("%d\n", best);
    
    return 0;
}