N = gets.to_i
s, e = gets.split(" ").map{|s| s.to_i}
stone = gets.split(" ").map{|s| s.to_i}

class UnionFind
	def initialize(n)
		@par = 0.upto(n-1).to_a
		@rank = Array.new(n, 0)
	end
	
	def unite(x, y)
		x = find(x)
		y = find(y)
		return if x == y
		if @rank[x] < @rank[y] then
			@par[x] = y
		else
			@par[y] = x
			@rank[x] += 1 if @rank[x] == @rank[y]
		end
	end
	
	def same?(x, y)
		find(x) == find(y)
	end
	
	private
	
	def find(x)
		if @par[x] == x then
			x
		else
			@par[x] = find(@par[x])
		end
	end
end

stone = [s] + stone + [e]

def getHaming(n)
	bit = 1
	haming = [n]
	32.times {
		haming << (n ^ bit)
		bit <<= 1
	}
	haming
end

uf = UnionFind.new(N+2)
v = Array.new(N+2) {Array.new}

stone.each_with_index {|x, i|
	haming = getHaming(x)
	(i+1).upto(N+1) {|j|
		if haming.include?(stone[j]) then
			uf.unite(i, j) 
			v[i] << j
			v[j] << i
		end
	}
}

if not uf.same?(0, N+1) then
	puts -1
else
	d = Array.new(N+2, Float::INFINITY)
	d[0] = 0
	q = [[0, 0]]
	while q.length > 0 do
		cv, c = q.shift
		v[cv].each {|nv|
			if d[nv] > c + 1 then
				d[nv] = c + 1
				q << [nv, c + 1]
			end
		}
	end
	puts d[N+1]-1
end