#include <bits/stdc++.h>
using namespace std;
long long modulo(long long base, long long exponent, long long modulus);
long long choose(long long n, long long k);
long long inverse(long long a, long long m);
void build();
long long ncr(long long n, long long r);
vector<long long> fact(1000010);
long long base[35];
void gauss(long long x) {
  for (long long i = 34; i >= 0; i--) {
    if (base[i] != -1 && (x & (1LL << i))) x ^= base[i];
  }
  if (x == 0) return;
  for (long long i = 34; i >= 0; i--) {
    if (x & (1LL << i)) {
      base[i] = x;
      return;
    }
  }
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  for (int i = 0; i < 35; i++) base[i] = -1;
  long long n;
  cin >> n;
  vector<long long> a(n);
  long long xorr = 0;
  for (int i = 0; i < n; i++) {
    cin >> a[i];
    gauss(a[i]);
    xorr ^= a[i];
  }
  if (xorr == 0) {
    cout << -1 << endl;
    return 0;
  }
  long long ans = 0;
  for (long long i = 0; i < 35; i++) {
    ans += (base[i] != -1);
  }
  cout << ans << endl;
  return 0;
}
long long ncr(long long n, long long r) {
  if (r > n || r < 0 || n < 0) return 0;
  long long ans = fact[n];
  long long temp = (fact[n - r] * fact[r]) % 1000000007;
  ans = (ans * inverse(temp, 1000000007)) % 1000000007;
  return ans;
}
void build() {
  fact[0] = 1;
  for (long long i = 1; i < 1000010; i++)
    fact[i] = (fact[i - 1] * i) % 1000000007;
}
long long modulo(long long base, long long exponent, long long modulus) {
  if (modulus == 1) return 0;
  long long result = 1;
  base = base % modulus;
  while (exponent > 0) {
    if (exponent % 2 == 1) {
      result = (result * base) % modulus;
    }
    exponent = exponent >> 1;
    base = (base * base) % modulus;
  }
  return result;
}
long long choose(long long n, long long k) {
  if (k == 0) return 1;
  return (n * choose(n - 1, k - 1)) / k;
}
void EE(long long a, long long b, long long &co1, long long &co2) {
  if (a % b == 0) {
    co1 = 0;
    co2 = 1;
    return;
  }
  EE(b, a % b, co1, co2);
  long long temp = co1;
  co1 = co2;
  co2 = temp - co2 * (a / b);
}
long long inverse(long long a, long long m) {
  long long x, y;
  EE(a, m, x, y);
  if (x < 0) x += m;
  return x;
}
