#ifndef ONLINE_JUDGE
#define _GLIBCXX_DEBUG
#endif
#include "atcoder/all"
#include <string>
#include <bits/stdc++.h>
#include <climits>
/*
Boostが使用したかったら WSLの方で開いて
#include <boost/multiprecision/cpp_dec_float.hpp>
#include <boost/multiprecision/cpp_int.hpp>
#include <boost/rational.hpp>
#include <boost/functional/hash.hpp>
// 任意長整数型
using Bint = boost::multiprecision::cpp_int;
// 仮数部が10進数で1024桁の浮動小数点数型(TLEしたら小さくする)
using BReal =
    boost::multiprecision::number<boost::multiprecision::cpp_dec_float<1024>>;
using Rat = boost::rational<Bint>;
*/
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
// 型エイリアスの設定
template<typename T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
using namespace atcoder;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<typename T> inline bool chmin(T &a, T b) { return ((a>b) ? (a = b, true) : (false));}
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define drep(i,n) for(int i=n-1;i>=0;i--)
#define REP(i,s,n) for(int i=s;i<(int)n;i++)
#define DREP(i,s,n) for(int i=n-1;i>=s;i--)
const long long inf = 1LL<<60;
const int infi = 1e9+1;
typedef long long ll;
typedef long double ld;
typedef __int128_t l3;
//cmpArg := 偏角ソート, atan2l(y, x); atan2l(y, x) = [-pi, pi]
#define cmpArg [](const auto &p1, const auto &p2) { return atan2l(p1.second, p1.first) < atan2l(p2.second, p2.first); }
typedef pair<int,int> pi;
typedef pair<ll,ll> pl;
#define vl vector<ll>
#define vvl vector<vector<ll>>
#define vi vector<int>
#define vvi vector<vector<int>>
#define vm vector<mint>
#define vvm vector<vector<mint>>
#define vvc vector<vector<char>>
#define vc vector<char>
#define vvpi vector<vector<pi>>
#define vpi vector<pi>
#define vpl vector<pl>
#define vvpl vector<vector<pl>>
#define pb push_back
#define eb emplace_back
#define YES cout<<"Yes"<<endl;
#define NO cout<<"No"<<endl;
#define YN { cout << "Yes" << endl; } else { cout << "No" << endl; }
#define all(x) x.begin(), x.end()
#define rall(i) std::rbegin(i), std::rend(i)
#define len(x) ((ll)(x).size())
#define fi first
#define se second
#define UNIQUE(x) sort(all(x)), x.erase(unique(all(x)), x.end())
int pc(ll x) { return __builtin_popcount(x); } //ビット列にどれだけ1がたっているかを求める pop count
void cincout(){  ios::sync_with_stdio(false);   std::cin.tie(nullptr);  cout<< fixed << setprecision(15);  }
bool out_grid(ll i, ll j, ll h, ll w) { return (!(0<=i && i<h && 0<=j && j<w)); }
inline void read(int &a) { std::cin >> a; }
inline void read(unsigned &a) { std::cin >> a; }
inline void read(long &a) { std::cin >> a; }
inline void read(long long &a) { std::cin >> a; }
inline void read(unsigned long long &a) { std::cin >> a; }
inline void read(char &a) { std::cin >> a; }
inline void read(float &a) { std::cin >> a; }
inline void read(double &a) { std::cin >> a; }
inline void read(long double &a) { std::cin >> a; }
inline void read(std::vector<bool> &vec) {
    for (int32_t i = 0; i < vec.size(); i++) {
        int a;
        read(a);
        vec[i] = a;
    }
}
inline void read(std::string &a) { std::cin >> a; }
template <class T>
inline void read(std::vector<T> &vec);
template <class T, size_t size>
inline void read(std::array<T, size> &vec);
template <class T, class L>
inline void read(std::pair<T, L> &p);
template <class T, size_t size>
inline void read(T (&vec)[size]);
template <class T>
inline void read(std::vector<T> &vec) {
    for (auto &i : vec) read(i);
}
template <class T>
inline void read(std::deque<T> &vec) {
    for (auto &i : vec) read(i);
}
template <class T, size_t size>
inline void read(std::array<T, size> &vec) {
    for (auto &i : vec) read(i);
}
template <class T, class L>
inline void read(std::pair<T, L> &p) {
    read(p.first);
    read(p.second);
}
template <class T, size_t size>
inline void read(T (&vec)[size]) {
    for (auto &i : vec) read(i);
}
template <class T>
inline void read(T &a) {
    std::cin >> a;
}
inline void in() {}
template <class Head, class... Tail>
inline void in(Head &head, Tail &...tail) {
    read(head);
    in(tail...);
}
inline void print() { std::cout << ' '; }
inline void print(const bool &a) { std::cout << a; }
inline void print(const int &a) { std::cout << a; }
inline void print(const unsigned &a) { std::cout << a; }
inline void print(const long &a) { std::cout << a; }
inline void print(const long long &a) { std::cout << a; }
inline void print(const unsigned long long &a) { std::cout << a; }
inline void print(const char &a) { std::cout << a; }
inline void print(const char a[]) { std::cout << a; }
inline void print(const float &a) { std::cout << a; }
inline void print(const double &a) { std::cout << a; }
inline void print(const long double &a) { std::cout << a; }
inline void print(const std::string &a) {
    for (auto &&i : a) print(i);
}
template <class T>
inline void print(const std::vector<T> &vec);
template <class T, size_t size>
inline void print(const std::array<T, size> &vec);
template <class T, class L>
inline void print(const std::pair<T, L> &p);
template <class T, size_t size>
inline void print(const T (&vec)[size]);
template <class T>
inline void print(const std::vector<T> &vec) {
    if (vec.empty()) return;
    print(vec[0]);
    for (auto i = vec.begin(); ++i != vec.end();) {
        std::cout << ' ';
        print(*i);
    }
}
template <class T>
inline void print(const std::deque<T> &vec) {
    if (vec.empty()) return;
    print(vec[0]);
    for (auto i = vec.begin(); ++i != vec.end();) {
        std::cout << ' ';
        print(*i);
    }
}
template <class T, size_t size>
inline void print(const std::array<T, size> &vec) {
    print(vec[0]);
    for (auto i = vec.begin(); ++i != vec.end();) {
        std::cout << ' ';
        print(*i);
    }
}
template <class T, class L>
inline void print(const std::pair<T, L> &p) {
    print(p.first);
    std::cout << ' ';
    print(p.second);
}
template <class T, size_t size>
inline void print(const T (&vec)[size]) {
    print(vec[0]);
    for (auto i = vec; ++i != end(vec);) {
        std::cout << ' ';
        print(*i);
    }
}
template <class T>
inline void print(const T &a) {
    std::cout << a;
}
inline void out() { std::cout << '\n'; }
template <class T>
inline void out(const T &t) {
    print(t);
    std::cout << '\n';
}
template <class Head, class... Tail>
inline void out(const Head &head, const Tail &...tail) {
    print(head);
    std::cout << ' ';
    out(tail...);
}
#define vec(type, name, ...) vector<type> name(__VA_ARGS__);
#define vv(type, name, h, ...) std::vector<std::vector<type>> name(h, std::vector<type>(__VA_ARGS__));
#define INT(...) int32_t __VA_ARGS__; in(__VA_ARGS__)
#define LL(...) int64_t __VA_ARGS__; in(__VA_ARGS__)
#define ULL(...) uint64_t __VA_ARGS__; in(__VA_ARGS__)
#define STR(...) std::string __VA_ARGS__; in(__VA_ARGS__)
#define CHR(...) char __VA_ARGS__; in(__VA_ARGS__)
#define LD(...) long double __VA_ARGS__; in(__VA_ARGS__)
#define VEC(type, name, size) std::vector<type> name(size); in(name)
#define VV(type, name, h, w) std::vector<std::vector<type>> name(h, std::vector<type>(w)); in(name)
template <class T>
ll sum(const T &a) {
    return accumulate(std::begin(a), std::end(a), 0LL);
}
template <class T>
ld dsum(const T &a) {
    return accumulate(std::begin(a), std::end(a), 0.0L);
}
template <class T>
auto min(const T &a) {
    return *min_element(std::begin(a), std::end(a));
}
template <class T>
auto max(const T &a) {
    return *max_element(std::begin(a), std::end(a));
}
template<typename T> T floor_div(const T n, const T d) {
    assert(d != 0);
    return n / d - static_cast<T>((n ^ d) < 0 && n % d != 0);
}
template<typename T> T ceil_div(const T n, const T d) {
    assert(d != 0);
    return n / d + static_cast<T>((n ^ d) >= 0 && n % d != 0);
}

using mint = modint998244353;

int main()
{
    INT(n);
    VEC(ll,a,n);
    //xorして0になるような集合を出す
    
    //基底を出す
    vi used(n,false); //基底に使用したか
    set<pl,greater<pl>> base;
    rep(i,len(a)) {
        ll x = a[i];
        for(auto [b,idx] : base) x = min(x, b^x);
        if(x>0) used[i] = true, base.emplace(x, a[i]);
    }

    rep(i,len(a)) if(!used[i]) {
        ll x = a[i];
        vi ans; ans.pb(i);
        for(auto [b,idx] : base) {
            if(chmin(x, b^x)) ans.pb(idx);
        }
        if(x == 0) {
            out(len(ans));
            rep(j,len(ans)) {
                cout << ans[j]+1 << (j == (len(ans)-1) ? '\n' : ' ');
            }
            return 0;
        }
    }
    out(-1);
}