#pragma region satashun
// #pragma GCC optimize("Ofast")
// #pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
using namespace std;

using uint = unsigned int;
using ll = long long;
using ull = unsigned long long;
using pii = pair<int, int>;
template <class T>
using V = vector<T>;
template <class T>
using VV = V<V<T>>;

template <class T>
V<T> make_vec(size_t a) {
    return V<T>(a);
}

template <class T, class... Ts>
auto make_vec(size_t a, Ts... ts) {
    return V<decltype(make_vec<T>(ts...))>(a, make_vec<T>(ts...));
}

template <typename T, typename V>
void fill_vec(T& v, const V& val) {
    v = val;
}

template <typename T, typename V>
void fill_vec(vector<T>& vec, const V& val) {
    for (auto& v : vec) fill_vec(v, val);
}

#define pb push_back
#define eb emplace_back
#define mp make_pair
#define fi first
#define se second
#define rep(i, n) rep2(i, 0, n)
#define rep2(i, m, n) for (int i = m; i < (n); i++)
#define per(i, b) per2(i, 0, b)
#define per2(i, a, b) for (int i = int(b) - 1; i >= int(a); i--)
#define ALL(c) (c).begin(), (c).end()
#define SZ(x) ((int)(x).size())

constexpr ll TEN(int n) { return (n == 0) ? 1 : 10 * TEN(n - 1); }

template <class T, class U>
void chmin(T& t, const U& u) {
    if (t > u) t = u;
}
template <class T, class U>
void chmax(T& t, const U& u) {
    if (t < u) t = u;
}

template <typename T>
int arglb(const V<T>& v, const T& x) {
    return distance(v.begin(), lower_bound(ALL(v), x));
}

template <typename T>
int argub(const V<T>& v, const T& x) {
    return distance(v.begin(), upper_bound(ALL(v), x));
}

template <class T>
void mkuni(vector<T>& v) {
    sort(ALL(v));
    v.erase(unique(ALL(v)), end(v));
}

template <class T>
vector<int> sort_by(const vector<T>& v, bool increasing = true) {
    vector<int> res(v.size());
    iota(res.begin(), res.end(), 0);

    if (increasing) {
        stable_sort(res.begin(), res.end(),
                    [&](int i, int j) { return v[i] < v[j]; });
    } else {
        stable_sort(res.begin(), res.end(),
                    [&](int i, int j) { return v[i] > v[j]; });
    }
    return res;
}

// prototype
template <class T, class U>
ostream& operator<<(ostream& os, const pair<T, U>& p);

template <class T>
ostream& operator<<(ostream& os, const vector<T>& v);

template <class T>
istream& operator>>(istream& is, vector<T>& v);

template <class T, size_t sz>
ostream& operator<<(ostream& os, const array<T, sz>& arr);

template <class T>
ostream& operator<<(ostream& os, const set<T>& ST);

template <class T>
ostream& operator<<(ostream& os, const multiset<T>& ST);

template <class T, class U>
ostream& operator<<(ostream& os, const map<T, U>& MP);

ostream& operator<<(ostream& o, __int128_t x);

// io functions
template <class T, class U>
istream& operator>>(istream& is, pair<T, U>& p) {
    is >> p.first >> p.second;
    return is;
}

template <class T, class U>
ostream& operator<<(ostream& os, const pair<T, U>& p) {
    os << "(" << p.first << "," << p.second << ")";
    return os;
}

template <class T>
istream& operator>>(istream& is, vector<T>& v) {
    for (auto& x : v) {
        is >> x;
    }
    return is;
}

template <class T>
ostream& operator<<(ostream& os, const vector<T>& v) {
    os << "{";
    rep(i, v.size()) {
        if (i) os << ",";
        os << v[i];
    }
    os << "}";
    return os;
}

template <class T, size_t sz>
ostream& operator<<(ostream& os, const array<T, sz>& arr) {
    os << '[';
    for (auto v : arr) os << v << ',';
    os << ']';
    return os;
}

template <class T>
ostream& operator<<(ostream& os, const set<T>& ST) {
    os << "{";
    for (auto it = ST.begin(); it != ST.end(); ++it) {
        if (it != ST.begin()) os << ",";
        os << *it;
    }
    os << "}";
    return os;
}

template <class T>
ostream& operator<<(ostream& os, const multiset<T>& ST) {
    os << "{";
    for (auto it = ST.begin(); it != ST.end(); ++it) {
        if (it != ST.begin()) os << ",";
        os << *it;
    }
    os << "}";
    return os;
}

template <class T, class U>
ostream& operator<<(ostream& os, const map<T, U>& MP) {
    for (auto it = MP.begin(); it != MP.end(); ++it) {
        os << "(" << it->first << ": " << it->second << ")";
    }
    return os;
}

string to_string(__int128_t x) {
    if (x == 0) return "0";
    string result;
    if (x < 0) {
        result += "-";
        x *= -1;
    }
    string t;
    while (x) {
        t.push_back('0' + x % 10);
        x /= 10;
    }
    reverse(t.begin(), t.end());
    return result + t;
}

ostream& operator<<(ostream& o, __int128_t x) { return o << to_string(x); }

#ifdef LOCAL
void debug_out() { cerr << endl; }
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
    cerr << " " << H;
    debug_out(T...);
}
#define debug(...) \
    cerr << __LINE__ << " [" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#define dump(x) cerr << __LINE__ << " " << #x << " = " << (x) << endl
#else
#define debug(...) (void(0))
#define dump(x) (void(0))
#endif

template <class T>
V<T>& operator+=(V<T>& vec, const T& v) {
    for (auto& x : vec) x += v;
    return vec;
}

template <class T>
V<T>& operator-=(V<T>& vec, const T& v) {
    for (auto& x : vec) x -= v;
    return vec;
}

// suc : 1 = newline, 2 = space
template <class T>
void print(T x, int suc = 1) {
    cout << x;
    if (suc == 1)
        cout << "\n";
    else if (suc == 2)
        cout << " ";
}

template <class T>
void print(const vector<T>& v, int suc = 1) {
    for (int i = 0; i < v.size(); ++i)
        print(v[i], i == int(v.size()) - 1 ? suc : 2);
}

template <class T>
void show(T x) {
    print(x, 1);
}

template <typename Head, typename... Tail>
void show(Head H, Tail... T) {
    print(H, 2);
    show(T...);
}

int topbit(int t) { return t == 0 ? -1 : 31 - __builtin_clz(t); }
int topbit(ll t) { return t == 0 ? -1 : 63 - __builtin_clzll(t); }
int botbit(int a) { return a == 0 ? 32 : __builtin_ctz(a); }
int botbit(ll a) { return a == 0 ? 64 : __builtin_ctzll(a); }
int popcount(int t) { return __builtin_popcount(t); }
int popcount(ll t) { return __builtin_popcountll(t); }
int bit_parity(int t) { return __builtin_parity(t); }
int bit_parity(ll t) { return __builtin_parityll(t); }

struct prepare_io {
    prepare_io() {
        cin.tie(nullptr);
        ios::sync_with_stdio(false);
        cout << fixed << setprecision(10);
    }
} prep_io;
#pragma endregion satashun

void slv() {
    // input
    int N;
    cin >> N;
    V<ll> A(N);
    cin >> A;

    // Let's solve!

    V<pair<ll, ll>> vec;
    V<int> ids = sort_by(A);

    rep(i, N) {
        ll x = A[ids[i]];
        ll b = 1ll << i;

        for (auto [v, mask] : vec) {
            if ((v ^ x) < x) {
                x ^= v;
                b ^= mask;
            }
        }
        if (x) {
            for (auto& [v, mask] : vec) {
                if ((v ^ x) < v) {
                    v ^= x;
                    mask ^= b;
                }
            }
            vec.eb(x, b);
        } else {
            V<int> ans;
            rep(j, 60) {
                if (b >> j & 1) ans.pb(ids[j]);
            }
            show(SZ(ans));
            ans += 1;
            show(ans);
            return;
        }
    }

    debug(vec);

    show(-1);
}

int main() {
    int cases = 1;
    // cin >> cases;
    rep(i, cases) slv();

    return 0;
}