#include <iostream>
#include <vector>
using namespace std;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int n;
    cin >> n;
    
    vector<long long> a(n);
    for(int i = 0; i < n; i++){
        cin >> a[i];
    }

    vector<pair<long long, long long>> basis;
    for(int i = 0; i < n; i++){
        long long value = a[i];
        long long index = (1LL << i);
        for(auto [base, ind]: basis){
            if((value ^ base) < value){
                value ^= base;
                index ^= ind;
            }
        }

        if(value == 0){
            vector<int> ans;
            for(int j = 0; j < 60; j++){
                if(index & (1LL << j)){
                    ans.emplace_back(j + 1);
                }
            }

            cout << ans.size() << endl;
            for(int b: ans){
                cout << b << " ";
            }
            cout << endl;
            return 0;
        }

        basis.emplace_back(value, index);
    }

    cout << -1 << endl;
}