using System;
using System.Linq;
using System.Collections.Generic;
//using System.Numerics;
using Debug = System.Diagnostics.Debug;
using SB = System.Text.StringBuilder;
using Number = System.Int64;
namespace Program {
    public class Solver {
        public void Solve() {
            var n = ri;
            var sum = 0L;
            var ans = 0;
            var a = new SortedSet<long>();
            foreach (var x in Enumerate(n, x => ri)) {
                sum ^= x;
                a.Add(2 * (x & -x) - 1);
            }
            for (int i = 30; i >= 0; i--)
                if ((sum >> i & 1) == 1 && a.Contains((1L << (i + 1)) - 1)) {
                    ans++;
                    sum ^= (1L << (i + 1)) - 1;
                }
            if (sum > 0) Console.WriteLine(-1);
            else Console.WriteLine(ans);
        }
        const long INF = 1L << 60;
        //int[] dx = { -1, 0, 1, 0 };
        //int[] dy = { 0, 1, 0, -1 };

        int ri { get { return sc.Integer(); } }
        long rl { get { return sc.Long(); } }
        double rd { get { return sc.Double(); } }
        string rs { get { return sc.Scan(); } }
        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 public void Swap<T>(ref T a, ref T b) {
            var tmp = a;
            a = b;
            b = tmp;
        }
    }
}

#region main

static class Ex {
    static public string AsString(this IEnumerable<char> ie) {
        return new string(ie.ToArray());
    }

    static public string AsJoinedString<T>(this IEnumerable<T> ie, string st = " ") {
        return string.Join(st, ie.Select(x => x.ToString()).ToArray());
        //return string.Join(st, ie);
    }

    static public void Main() {
        Console.SetOut(new Program.IO.Printer(Console.OpenStandardOutput()) { AutoFlush = false });
        var solver = new Program.Solver();
        solver.Solve();
        Console.Out.Flush();
    }
}

#endregion
#region Ex

namespace Program.IO {
    using System.IO;
    using System.Text;
    using System.Globalization;

    public class Printer: StreamWriter {
        public override IFormatProvider FormatProvider {
            get { return CultureInfo.InvariantCulture; }
        }
        public Printer(Stream stream) : base(stream, new UTF8Encoding(false, true)) { }
    }

    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 = false;
        public bool IsEndOfStream {
            get { return isEof; }
        }

        private byte read() {
            if (isEof) return 0;
            if (ptr >= len) {
                ptr = 0;
                if ((len = str.Read(buf, 0, 1024)) <= 0) {
                    isEof = true;
                    return 0;
                }
            }
            return buf[ptr++];
        }

        public char Char() {
            byte b = 0;
            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 != 0; b = (char)read()) if (b != '\r') sb.Append(b);
            return sb.ToString();
        }

        public long Long() {
            return isEof ? long.MinValue : long.Parse(Scan());
        }

        public int Integer() {
            return isEof ? int.MinValue : int.Parse(Scan());
        }

        public double Double() {
            return isEof ? double.NaN : double.Parse(Scan(), CultureInfo.InvariantCulture);
        }
    }
}

#endregion


Measured memory_bytes: 17748