local ffi = require("ffi")
local C = ffi.C
ffi.cdef[[
long long atoll(const char*);
]]

local function lltonumber(str)
  return C.atoll(str)
end

local n = io.read("*n", "*l")
local t = {}
for i = 1, 63 do t[i] = false end
local s = io.read()
for w in s:gmatch("%d+") do
  local num = lltonumber(w)
  for j = 1, 63 do
    if num % 2LL == 1LL then
      t[j] = true
    end
    num = num / 2LL
  end
end
local ret = 1LL
for i = 1, 63 do
  if not t[i] then
    ret = tostring(ret):gsub("LL", "")
    print(ret) os.exit()
  end
  ret = ret * 2LL
end