// yukicoder: No.698 ペアでチームを作ろう
// 2019.7.20 bal4u

#include <stdio.h>
#include <string.h>

#if 1
#define gc() getchar_unlocked()
#else
#define gc() getchar()
#endif

int in() {   // 非負整数の入力
	int n = 0, c = gc();
	do n = 10 * n + (c & 0xf); while ((c = gc()) >= '0');
	return n;
}

int a[16], N;
int dp[(1 << 14)+10];

int main()
{
	int i, u, v, lim;

	N = in();
	for (i = 0; i < N; i++) a[i] = in();
	lim = (1 << N);
	memset(dp, -1, sizeof(int)*lim);
	dp[0] = 0;
	for (i = 0; i < lim; i++) if (dp[i] >= 0) {
		for (u = 0; u < N; u++) if (!((i >> u) & 1)) {
			for (v = u+1; v < N; v++) if (!((i >> v) & 1)) {
				int *t = &dp[i | (1 << u) | (1 << v)];
				int x = dp[i] + (a[u] ^ a[v]);
				if (*t < x) *t = x;
			}
		}
	}
	printf("%d\n", dp[lim-1]);
	return 0;
}