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<Integer, Integer> map = new HashMap<>();
        ArrayList<ArrayList<Integer>> graph = new ArrayList<>();
        for (int i = 0; i < n + 2; i++) {
            map.put(sc.nextInt(), i);
            graph.add(new ArrayList<>());
        }
        for (int x : map.keySet()) {
            for (int i = 0; i < 30; i++) {
                if (map.containsKey(x ^ (1 << i))) {
                    graph.get(map.get(x)).add(map.get(x ^ (1 << i)));
                }
            }
        }
        PriorityQueue<Path> queue = new PriorityQueue<>();
        queue.add(new Path(0, 0));
        int[] costs = new int[n + 2];
        Arrays.fill(costs, Integer.MAX_VALUE);
        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 getPop(int x) {
        int pop = 0;
        while (x > 0) {
            pop += x % 2;
            x >>= 1;
        }
        return pop;
    }
    
    static class Path implements Comparable<Path> {
        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 String next() throws Exception {
        if (!st.hasMoreTokens()) {
            st = new StringTokenizer(br.readLine());
        }
        return st.nextToken();
    }
}