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(); int[] values = new int[n + 2]; values[0] = sc.nextInt(); values[1] = sc.nextInt(); for (int i = 2; i <= n + 1; i++) { values[i] = sc.nextInt(); } ArrayList> graph = new ArrayList<>(); for (int i = 0; i < n + 2; i++) { graph.add(new ArrayList<>()); } for (int i = 0; i < n + 1; i++) { for (int j = i + 1; j < n + 2; j++) { if (getHumming(values[i], values[j]) <= 1) { graph.get(i).add(j); graph.get(j).add(i); } } } int[] costs = new int[n + 2]; Arrays.fill(costs, Integer.MAX_VALUE); PriorityQueue queue = new PriorityQueue<>(); queue.add(new Path(0, 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[1] == Integer.MAX_VALUE) { System.out.println(-1); } else { System.out.println(costs[1] - 1); } } static int getHumming(int x, int y) { int humming = 0; while (x > 0 || y > 0) { humming += Math.abs(x % 2 - y % 2); x >>= 1; y >>= 1; } return humming; } 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 { if (!st.hasMoreTokens()) { st = new StringTokenizer(br.readLine()); } return st.nextToken(); } }