using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using static System.Console;
using static System.Math;
//using CS_Contest.Graph;
using CS_Contest.Loop;
using CS_Contest.Utils;
using static Nakov.IO.Cin;
using static CS_Contest.IO.IO;
using static CS_Contest.Utils.MyMath;
namespace CS_Contest {
using Li = List<int>;
using LLi = List<List<int>>;
using Ll = List<long>;
using ti3 = Tuple<int, int, int>;
using ti2 = Tuple<int, int>;
internal class Program {
private static void Main(string[] args) {
var sw = new StreamWriter(OpenStandardOutput()) { AutoFlush = false };
SetOut(sw);
new Calc().Solve();
Out.Flush();
}
public class Calc
{
public void Solve() {
var N = NextInt();
var A = new Li();
N.REP(i=>A.Add(NextInt()));
var box = new bool[30];
var sum = 0;
Func<int, int> Ctz = (x) =>
{
var rt = 0;
while (x % 2 == 0) {
rt++;
x >>= 1;
}
return rt;
};
A.ForEach(ai =>
{
sum ^= ai;
box[Ctz(ai)] = true;
});
int res = 0;
for (int i = 29; i >= 0; i--) {
if ((sum & (1 << i))!=0) {
if (!box[i]) {
res = -1;
break;
}
else {
res++;
sum^= (1 << (i + 1)) - 1;
}
}
}
res.WL();
}
}
}
}
namespace Nakov.IO {
using System;
using System.Text;
using System.Globalization;
public static class Cin {
public static string NextToken() {
StringBuilder tokenChars = new StringBuilder();
bool tokenFinished = false;
bool skipWhiteSpaceMode = true;
while (!tokenFinished) {
int nextChar = Console.Read();
if (nextChar == -1) {
tokenFinished = true;
} else {
char ch = (char)nextChar;
if (char.IsWhiteSpace(ch)) {
if (!skipWhiteSpaceMode) {
tokenFinished = true;
if (ch == '\r' && (Environment.NewLine == "\r\n")) {
Console.Read();
}
}
} else {
skipWhiteSpaceMode = false;
tokenChars.Append(ch);
}
}
}
string token = tokenChars.ToString();
return token;
}
public static int NextInt() {
string token = Cin.NextToken();
return int.Parse(token);
}
public static long NextLong() {
string token = Cin.NextToken();
return long.Parse(token);
}
public static double NextDouble(bool acceptAnyDecimalSeparator = true) {
string token = Cin.NextToken();
if (acceptAnyDecimalSeparator) {
token = token.Replace(',', '.');
double result = double.Parse(token, CultureInfo.InvariantCulture);
return result;
} else {
double result = double.Parse(token);
return result;
}
}
public static decimal NextDecimal(bool acceptAnyDecimalSeparator = true) {
string token = Cin.NextToken();
if (acceptAnyDecimalSeparator) {
token = token.Replace(',', '.');
decimal result = decimal.Parse(token, CultureInfo.InvariantCulture);
return result;
} else {
decimal result = decimal.Parse(token);
return result;
}
}
}
}
namespace CS_Contest.Loop {
[DebuggerStepThrough]
public static class Loop {
public static void REP(this int n, Action<int> act) {
for (var i = 0; i < n; i++) {
act(i);
}
}
public static void ForeachWith<T>(this IEnumerable<T> ie, Action<int, T> act) {
var i = 0;
foreach (var item in ie) {
act(i, item);
i++;
}
}
public static void Foreach<T>(this IEnumerable<T> ie, Action<T> act) {
foreach (var item in ie) {
act(item);
}
}
}
public class Generate
{
public static IEnumerable<int> Seq(int s, int e) => Seq(s, e, 1);
public static IEnumerable<int> Seq(int s, int e, int a) {
while (s != e) {
yield return s;
s += a;
}
}
public static List<T> Repeat<T>(Func<int, T> result, int range) =>
Enumerable.Range(0, range).Select(result).ToList();
}
}
namespace CS_Contest.IO {
using Li = List<int>;
using Ll = List<long>;
public static class IO {
public static void WL(this object obj) => WriteLine(obj);
public static void WL(this string obj) => WriteLine(obj);
public static void WL<T>(this IEnumerable<T> list) => list.ToList().ForEach(x => x.WL());
public static Li NextIntList() => ReadLine().Split().Select(int.Parse).ToList();
public static Ll NextLongList() => ReadLine().Split().Select(long.Parse).ToList();
public static T Tee<T>(this T t, Func<T, string> formatter = null) {
if (formatter == null) formatter = arg => arg.ToString();
formatter(t).WL();
return t;
}
public static void JoinWL<T>(this IEnumerable<T> @this, string sp = " ") => @this.StringJoin(sp).WL();
public static void W(this object @this) => Write(@this);
}
}
namespace CS_Contest.Utils {
using Li = List<int>;
using Ll = List<long>;
[DebuggerStepThrough]
public static class Utils {
public static bool Within(int x, int y, int lx, int ly) => !(x < 0 || x >= lx || y < 0 || y >= ly);
public static void Add<T1, T2>(this List<Tuple<T1, T2>> list, T1 t1, T2 t2) => list.Add(new Tuple<T1, T2>(t1, t2));
public static string StringJoin<T>(this IEnumerable<T> l, string separator = "") => string.Join(separator, l);
public static Queue<T> ToQueue<T>(this IEnumerable<T> iEnumerable) {
var rt = new Queue<T>();
foreach (var item in iEnumerable) {
rt.Enqueue(item);
}
return rt;
}
public static void Swap<T>(ref T x, ref T y) {
var tmp = x;
x = y;
y = tmp;
}
public static Dictionary<TKey, int> CountUp<TKey>(this IEnumerable<TKey> l) {
var dic = new Dictionary<TKey, int>();
foreach (var item in l) {
if (dic.ContainsKey(item)) dic[item]++;
else dic.Add(item, 1);
}
return dic;
}
public static int Count<T>(this IEnumerable<T> l, T target) => l.Count(x => x.Equals(target));
public static IEnumerable<T> SkipAt<T>(this IEnumerable<T> @this, int at) {
var enumerable = @this as T[] ?? @this.ToArray();
for (var i = 0; i < enumerable.Count(); i++) {
if (i == at) continue;
yield return enumerable.ElementAt(i);
}
}
}
public class Map<TKey, TValue> : Dictionary<TKey, TValue> {
public Map() : base() { }
public Map(int capacity) : base(capacity) { }
public new TValue this[TKey index] {
get {
TValue v;
return this.TryGetValue(index, out v) ? v : base[index] = default(TValue);
}
set { base[index] = value; }
}
}
public static class MyMath {
public static T EMin<T>(params T[] a) where T : IComparable<T> => a.Min();
public static T EMax<T>(params T[] a) where T : IComparable<T> => a.Max();
}
}