/* -*- coding: utf-8 -*-
 *
 * 2895.cc:  No.2895 Zero XOR Subset - yukicoder
 */

#include<cstdio>
#include<algorithm>

using namespace std;

/* constant */

const int BN = 60;
const int MAX_N = BN + 1;

/* typedef */

using ll = long long;

/* global variables */

ll as[MAX_N], bs[MAX_N];

/* subroutines */

inline int biti(ll a, int i) { return (a >> i) & 1; }

/* main */

int main() {
  int n;
  scanf("%d", &n);
  n = min(BN + 1, n);
  
  for (int i = 0; i < n; i++) scanf("%lld", as + i);
  for (int i = 0; i < n; i++) bs[i] = (1LL << i);

  for (int i = 0, u = 0; u < n && i < BN; i++) {
    if (! biti(as[u], i)) {
      for (int v = u + 1; v < n; v++)
	if (biti(as[v], i)) {
	  swap(as[u], as[v]); swap(bs[u], bs[v]);
	  break;
	}
    }

    if (biti(as[u], i)) {
      for (int v = u + 1; v < n; v++)
	if (biti(as[v], i))
	  as[v] ^= as[u], bs[v] ^= bs[u];
      u++;
    }
  }

  int xi = -1;
  for (int i = 0; xi < 0 && i < n; i++)
    if (as[i] == 0) xi = i;

  if (xi >= 0) {
    ll bx = bs[xi];
    int m = 0;
    for (int i = 0; i < BN; i++)
      if (biti(bx, i)) bs[m++] = i;

    printf("%d\n", m);
    for (int i = 0; i < m; i++)
      printf("%lld%c", bs[i] + 1, (i + 1 < m) ? ' ' : '\n');
  }
  else
    puts("-1");
  
  return 0;
}