#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
#define rep(i, n) for(int i=0;i<(n);++i)
#define rep1(i, n) for(int i=1;i<=(n);i++)
#define ll long long
using mint = modint998244353;
using P = pair<ll,ll>;
using lb = long double;
using T = tuple<ll, ll, ll>;
#ifdef LOCAL
#  include <debug_print.hpp>
#  define dbg(...) debug_print::multi_print(#__VA_ARGS__, __VA_ARGS__)
#else
#  define dbg(...) (static_cast<void>(0))
#endif

int main()
{
    int n;
    cin >> n;
    vector<ll> a(n);
    rep(i,n) cin >> a[i];
    auto b = a;
    vector<vector<int>> g(n);
    for(int i=60;i>=0;i--){
        bool found = false;
        ll s = 1ll<<i+1;
        int r = -1;
        dbg(s);
        for(int j=0;j<n;j++) {
            if((a[j]>>i&1) && a[j]<s) {
                found = true;
                r = j;
                break;
            }
        }
        dbg(found);
        if(found) {
            rep(j,n) {
                if(j!=r && a[j]>>i&1) {
                    a[j] ^= a[r];
                    g[j].push_back(r);
                }
            }
        }
    }
    dbg(a);
    for(int i=0;i<n;i++) {
        if(a[i]==0) {
            queue<int> q;
            q.push(i);
            vector<int> ans;
            while(!q.empty()) {
                int u = q.front();q.pop();
                ans.push_back(u);
                for(int v : g[u]) {
                    q.push(v);
                }
            }
            ll s = 0;
            cout << ans.size() << endl;
            for(int ad : ans) {
                cout << ad+1 << " ";
                s ^= b[ad];
            }
            assert(s==0);
            cout << endl;
            return 0;
        }
    }
    cout << -1 << endl;
    return 0;
}