import sequtils,algorithm
template `max=`*(x,y) = x = max(x,y)
template `min=`*(x,y) = x = min(x,y)

proc getchar_unlocked():char {. importc:"getchar_unlocked",header: "<stdio.h>" .}
proc scan(): int =
  while true:
    let k = getchar_unlocked()
    if k < '0': break
    result = 10 * result + k.ord - '0'.ord

# 14C2 * 12C2 * 10C2 * 8C2 * 6C2 * 4C2 * 2C2
# 高々:1*6*15*28*45*66*91 なので全て列挙
# proc test() =
#   var A = toSeq(1..6)
#   while true:
#     echo A
#     # A.reverse(A.len div 2, A.len - 1)
#     if not A.nextPermutation(): return
# test()
let n = scan()
let A = newSeqWith(n,scan())
proc solve(A:seq[int]) : int =
  var A = A.sorted(cmp)
  while true:
    var s = 0
    for i in 0..<n div 2:
      s = s xor ( A[i] + A[i + n div 2])
    result .max= s
    A.reverse(n div 2,A.len-1)
    if not A.nextPermutation() : return
echo solve(A)