using System;
using System.Linq;
using System.Collections.Generic;
using Debug = System.Diagnostics.Debug;
using SB = System.Text.StringBuilder;
//using System.Numerics;
using Number = System.Int64;
using static System.Math;
using C = System.Int32;
using V = System.Int32;
//using static MathEx;
//using P = System.Collections.Generic.KeyValuePair<int, int>;
namespace Program
{
public class Solver
{
public void Solve()
{
var n = ri;
var a = Enumerate(n, x => rl);
var sum = 0L;
foreach (var x in a) sum ^= x;
var has = new bool[60];
foreach (var x in a)
{
for (int j = 0; j < 60; j++)
if ((x >> j & 1) == 1) { has[j] = true; break; }
}
var cnt = 0;
for (int i = 60 - 1; i >= 0; i--)
{
if ((sum >> i & 1) == 1)
{
cnt++;
if (has[i]) sum ^= (1L << i) ^ ((1L << i) - 1);
else
{
IO.Printer.Out.WriteLine(-1);
return;
}
}
}
IO.Printer.Out.WriteLine(cnt);
}
//*
int ri => sc.Integer();
long rl => sc.Long();
double rd => sc.Double();
string rs => sc.Scan();
char rc => sc.Char();
[System.Diagnostics.Conditional("DEBUG")]
void put(params object[] a) => Debug.WriteLine(string.Join(" ", a));
//*/
public IO.StreamScanner sc = new IO.StreamScanner(Console.OpenStandardInput());
static T[] Enumerate<T>(int n, Func<int, T> f)
{
var a = new T[n];
for (int i = 0; i < n; ++i) a[i] = f(i);
return a;
}
static void Swap<T>(ref T a, ref T b)
{
var tmp = a;
a = b;
b = tmp;
}
}
}
#region main
static class Ex
{
public static string AsString(this IEnumerable<char> ie)
{
return new string(ie.ToArray());
}
public static string AsJoinedString<T>(this IEnumerable<T> ie, string st = " ")
{
return string.Join(st, ie);
}
public static void Main()
{
var solver = new Program.Solver();
solver.Solve();
Program.IO.Printer.Out.Flush();
}
}
#endregion
#region Ex
namespace Program.IO
{
using System.IO;
using System.Text;
using System.Globalization;
public class Printer: StreamWriter
{
static Printer()
{
Out = new Printer(Console.OpenStandardOutput()) { AutoFlush = false };
}
public static Printer Out { get; set; }
public override IFormatProvider FormatProvider
{
get { return CultureInfo.InvariantCulture; }
}
public Printer(Stream stream) : base(stream, new UTF8Encoding(false, true))
{
}
public Printer(Stream stream, Encoding encoding) : base(stream, encoding)
{
}
public void Write<T>(string format, T[] source)
{
base.Write(format, source.OfType<object>().ToArray());
}
public void WriteLine<T>(string format, T[] source)
{
base.WriteLine(format, source.OfType<object>().ToArray());
}
}
public class StreamScanner
{
public StreamScanner(Stream stream)
{
str = stream;
}
public readonly Stream str;
private readonly byte[] buf = new byte[1024];
private int len, ptr;
public bool isEof;
public bool IsEndOfStream
{
get { return isEof; }
}
private byte read()
{
if (isEof) return 0;
if (ptr < len) return buf[ptr++];
ptr = 0;
if ((len = str.Read(buf, 0, 1024)) > 0) return buf[ptr++];
isEof = true;
return 0;
}
public char Char()
{
byte b;
do b = read(); while ((b < 33 || 126 < b) && !isEof);
return (char)b;
}
public string Scan()
{
var sb = new StringBuilder();
for (var b = Char(); b >= 33 && b <= 126; b = (char)read())
sb.Append(b);
return sb.ToString();
}
public string ScanLine()
{
var sb = new StringBuilder();
for (var b = Char(); b != '\n'; b = (char)read())
if (b == 0) break;
else if (b != '\r') sb.Append(b);
return sb.ToString();
}
public long Long()
{
if (isEof) return long.MinValue;
long ret = 0;
byte b;
var ng = false;
do b = read(); while (b != 0 && b != '-' && (b < '0' || '9' < b));
if (b == 0) return long.MinValue;
if (b == '-')
{
ng = true;
b = read();
}
for (; ; b = read())
{
if (b < '0' || '9' < b)
return ng ? -ret : ret;
ret = ret * 10 + b - '0';
}
}
public int Integer()
{
return (isEof) ? int.MinValue : (int)Long();
}
public double Double()
{
var s = Scan();
return s != "" ? double.Parse(s, CultureInfo.InvariantCulture) : double.NaN;
}
static T[] enumerate<T>(int n, Func<T> f)
{
var a = new T[n];
for (int i = 0; i < n; ++i) a[i] = f();
return a;
}
public char[] Char(int n)
{
return enumerate(n, Char);
}
public string[] Scan(int n)
{
return enumerate(n, Scan);
}
public double[] Double(int n)
{
return enumerate(n, Double);
}
public int[] Integer(int n)
{
return enumerate(n, Integer);
}
public long[] Long(int n)
{
return enumerate(n, Long);
}
}
}
#endregion