#include <bits/stdc++.h>
using namespace std;
using ll = long long;

const int MAX_BITS = 60;
vector<ll> basis(MAX_BITS, 0);  // Linear basis array of size 60
vector<int> basis_idx(MAX_BITS); // To store one index corresponding to each basis vector

// Function to insert number into the basis
bool insertBasis(ll x, int idx) {
    vector<int> result;
    for (int i = MAX_BITS - 1; i >= 0; --i) {
        if (!(x & (1LL << i))) continue; // Skip if bit is not set

        if (!basis[i]) {  // If this bit is not yet in the basis
            basis[i] = x;
            basis_idx[i] = idx;  // Store the index of this element
            return true;         // Inserted successfully
        }

        // Reduce x by the basis element
        x ^= basis[i];
        result.push_back(basis_idx[i]);
    }

    // If x becomes 0, it means this element is a combination of basis elements
    result.push_back(idx);

    // Output the result indices
    printf("%d\n", (int)result.size());
    for (int i : result) {
        printf("%d ", i + 1);  // Output 1-based index
    }
    printf("\n");
    return false;  // This element was not added to the basis
}

int main() {
    int n;
    scanf("%d", &n);
    vector<ll> a(n);

    // Input the array
    for (int i = 0; i < n; ++i) {
        scanf("%lld", &a[i]);
    }

    // Insert each element into the basis
    for (int i = 0; i < n; ++i) {
        if (a[i] == 0) {  // Handle edge case where element is already zero
            printf("1\n%d\n", i + 1);
            return 0;
        }
        if (!insertBasis(a[i], i)) {
            return 0;  // Found a subset that XORs to zero, so stop
        }
    }

    // If no zero XOR subset was found, output -1
    puts("-1");
    return 0;
}