import java.io.*;
import java.util.*;
import java.util.function.*;
import java.util.stream.*;

public class Main {
    static List<Set<Long>> visited = new ArrayList<>();
    static long[] values;
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        int n = Math.min(sc.nextInt(), 100);
        values = new long[n];
        for (int i = 0; i < n; i++) {
            values[i] = sc.nextLong();
            visited.add(new HashSet<>());
        }
        for (int i = n - 1; i >= 0; i--) {
            List<Integer> ans = dfw(i - 1, values[i]);
            if (ans != null) {
                ans.add(i + 1);
                System.out.println(ans.size());
                System.out.println(ans.stream().map(x -> x.toString()).collect(Collectors.joining(" ")));
                return;
            }
        }
        System.out.println(-1);
    }
    
    static List<Integer> dfw(int idx, long v) {
        if (v == 0) {
            return new ArrayList<>();
        }
        if (idx < 0) {
            return null;
        }
        if (!visited.get(idx).contains(v)) {
            visited.get(idx).add(v);
            List<Integer> current = dfw(idx - 1, v);
            if (current != null) {
                return current;
            }
            current = dfw(idx - 1, v ^ values[idx]);
            if (current != null) {
                current.add(idx + 1);
                return current;
            }
        }
        return null;
    }
}

class Scanner {
    BufferedReader br;
    StringTokenizer st = new StringTokenizer("");

    public Scanner() {
        try {
            br = new BufferedReader(new InputStreamReader(System.in));
        } catch (Exception e) {
            
        }
    }
    
    public int nextInt() {
        return Integer.parseInt(next());
    }
    
    public long nextLong() {
        return Long.parseLong(next());
    }
    
    public double nextDouble() {
        return Double.parseDouble(next());
    }
    
    public String next() {
        try {
            while (!st.hasMoreTokens()) {
                st = new StringTokenizer(br.readLine());
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            return st.nextToken();
        }
    }
    
}