import strutils, sequtils

let n = parseInt(readLine(stdin))
let a = map(readLine(stdin).split(), parseInt)
var answer: int = 1
var tmp: int = 0

while true:
  tmp = 0
  for i in 0..<n:
    if (a[i] xor answer) == a[i] + answer:
      tmp += 1
  if tmp == n:
    echo answer
    break
  else:
    answer *= 2