import std.algorithm, std.container, std.conv, std.math, std.range, std.typecons, std.stdio, std.string;
import std.bitmanip;

auto rdsp(){return readln.splitter;}
void pick(R,T)(ref R r,ref T t){t=r.front.to!T;r.popFront;}
void readV(T...)(ref T t){auto r=rdsp;foreach(ref v;t)pick(r,v);}
void readA(T)(size_t n,ref T[]t){t=new T[](n);auto r=rdsp;foreach(ref v;t)pick(r,v);}

void main()
{
  int n; readV(n);
  int[] a; readA(n, a);

  auto r = 0, mask = (1<<n)-1;
  foreach (i; 0..1<<n) {
    if (i.popcnt != n/2) continue;

    auto b = i.bitsSet.array, c = (~i&mask).bitsSet.array;
    foreach (d; c.permutations) {
      auto s = 0;
      foreach (j; 0..n/2) s ^= a[b[j]]+a[d[j]];
      r = max(r, s);
    }
  }

  writeln(r);
}

pragma(inline) {
  pure bool bitTest(T)(T n, size_t i) { return (n & (T(1) << i)) != 0; }
  pure T bitSet(T)(T n, size_t i) { return n | (T(1) << i); }
  pure T bitReset(T)(T n, size_t i) { return n & ~(T(1) << i); }
  pure T bitComp(T)(T n, size_t i) { return n ^ (T(1) << i); }

  pure T bitSet(T)(T n, size_t s, size_t e) { return n | ((T(1) << e) - 1) & ~((T(1) << s) - 1); }
  pure T bitReset(T)(T n, size_t s, size_t e) { return n & (~((T(1) << e) - 1) | ((T(1) << s) - 1)); }
  pure T bitComp(T)(T n, size_t s, size_t e) { return n ^ ((T(1) << e) - 1) & ~((T(1) << s) - 1); }

  import core.bitop;
  pure int bsf(T)(T n) { return core.bitop.bsf(ulong(n)); }
  pure int bsr(T)(T n) { return core.bitop.bsr(ulong(n)); }
  pure int popcnt(T)(T n) { return core.bitop.popcnt(ulong(n)); }
}