import java.io.*; import java.util.*; public class Main { public static void main(String[] args) throws Exception { Scanner sc = new Scanner(); int n = sc.nextInt(); HashMap idxes = new HashMap<>(); int[] values = new int[n + 2]; values[n] = sc.nextInt(); idxes.put(values[n], n); values[n + 1] = sc.nextInt(); idxes.put(values[n + 1], n + 1); ArrayList> graph = new ArrayList<>(); graph.add(new ArrayList<>()); graph.add(new ArrayList<>()); for (int i = 0; i < n; i++) { values[i] = sc.nextInt(); idxes.put(values[i], i); graph.add(new ArrayList<>()); } for (int i = 0; i <= n + 1; i++) { int x = values[i]; for (int j = 0; j < 30; j++) { x ^= (1 << j); if (idxes.containsKey(x)) { graph.get(idxes.get(x)).add(i); } x ^= (1 << j); } } PriorityQueue queue = new PriorityQueue<>(); int[] costs = new int[n + 2]; Arrays.fill(costs, Integer.MAX_VALUE); queue.add(new Path(n, 0)); while (queue.size() > 0) { Path p = queue.poll(); if (costs[p.idx] < p.value) { continue; } costs[p.idx] = p.value; for (int x : graph.get(p.idx)) { queue.add(new Path(x, p.value + 1)); } } if (costs[n + 1] == Integer.MAX_VALUE) { System.out.println(-1); } else { System.out.println(costs[n + 1] - 1); } } static class Path implements Comparable { int idx; int value; public Path(int idx, int value) { this.idx = idx; this.value = value; } public int compareTo(Path another) { return value - another.value; } } } class Scanner { BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); StringTokenizer st = new StringTokenizer(""); public Scanner() throws Exception { } public int nextInt() throws Exception { return Integer.parseInt(next()); } public long nextLong() throws Exception { return Long.parseLong(next()); } public double nextDouble() throws Exception { return Double.parseDouble(next()); } public String next() throws Exception { while (!st.hasMoreTokens()) { st = new StringTokenizer(br.readLine()); } return st.nextToken(); } }