#include <bits/stdc++.h>
using namespace std;
template <class U, class T>
void Max(U &first, T second) {
  if (first < second) first = second;
}
template <class U, class T>
void Min(U &first, T second) {
  if (first > second) first = second;
}
template <class T>
void add(int &a, T b) {
  a = (a + b) % 1000000007;
}
inline int gcd(int a, int b) { return b == 0 ? a : gcd(b, a % b); }
inline long long gcd(long long a, long long b) {
  return b == 0 ? a : gcd(b, a % b);
}
int pow(int a, int b) {
  int ans = 1;
  while (b) {
    if (b & 1) ans = 1LL * ans * a % 1000000007;
    a = 1LL * a * a % 1000000007;
    b >>= 1;
  }
  return ans;
}
int pow(int a, int b, int c) {
  int ans = 1;
  while (b) {
    if (b & 1) ans = 1LL * ans * a % c;
    a = 1LL * a * a % c;
    b >>= 1;
  }
  return ans;
}
int a[200010];
int main() {
  int ca = 0, T, k, i, j, m = 0, K, n;
  double start = clock();
  scanf("%d", &n);
  int s = 0;
  for (int i = 0; i < n; i++) {
    scanf("%d", &a[i]);
    if (a[i] == 0)
      i--, n--;
    else
      s ^= a[i];
  }
  if (s == 0) {
    puts("-1");
    return 0;
  }
  if (n == 1) {
    puts("1");
    return 0;
  }
  sort(a, a + n);
  int sz = 0;
  for (int i = 0; i < n; i++) {
    j = i;
    while (j < n && a[j] == a[i]) j++;
    if ((j - i) & 1) a[m++] = a[i];
    i = j - 1;
    sz++;
  }
  if (sz == 1) {
    puts("1");
    return 0;
  }
  int v[32] = {0}, ans = 0;
  for (int i = 0; i < m; i++) {
    int first = a[i];
    for (int j = 31 - 1; j >= 0; j--)
      if (first >> j & 1) {
        if (!v[j]) {
          v[j] = first;
          break;
        } else
          first ^= v[j];
      }
  }
  for (int j = 0; j < 31; j++)
    if (v[j]) ans++;
  Max(ans, 2);
  printf("%d\n", ans);
  cerr << (1. * clock() - start) / CLOCKS_PER_SEC << "\n";
}
