local bxor = bit.bxor
local f = {}
do
  local mul = 1
  while true do
    table.insert(f, mul)
    mul = mul * 2
    if 1000000007 < mul then break end
  end
end

local n = io.read("*n")
local a = {}
a[1], a[2] = io.read("*n", "*n")
for i = 3, n + 2 do
  a[i] = io.read("*n")
end
n = n + 2
local len = {}
local ainv = {}
for i = 1, n do
  len[i] = -1
  ainv[a[i]] = i
end
len[1] = 0
local tasks = {1}
local done = 0
while done < #tasks do
  done = done + 1
  local src = tasks[done]
  for i = 1, #f do
    local d = bxor(a[src], f[i])
    local dst = ainv[d]
    if dst and len[dst] < 0 then
      if dst == 2 then
        print(len[src])
        os.exit()
      end
      len[dst] = len[src] + 1
      table.insert(tasks, dst)
    end
  end
end
print(-1)