using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using static System.Console;
using static System.Math;

namespace AtTest._700problems
{
    class CodeFestival2017C_D
    {
        static void Main(string[] args)
        {
            var sw = new System.IO.StreamWriter(OpenStandardOutput()) { AutoFlush = false };
            SetOut(sw);

            Method(args);

            Out.Flush();
        }

        static void Method(string[] args)
        {
            string s = Read();

            var dict = new Dictionary<int, int>();
            dict.Add(0, 1);
            for(int i = 0; i <= 26; i++)
            {
                dict.Add(1 << i, 1);
            }
            int now = 0;
            for (int i = 0; i < s.Length; i++)
            {
                int tmp = 1 << (s[i] - 'a');
                int next = now ^ tmp;
                if (!dict.ContainsKey(next))
                {
                    dict.Add(next, int.MaxValue / 2);
                }
                dict[next] = Min(dict[next], dict[now] + 1);
                now = next;
            }
            WriteLine(dict[now]);
        }

        private static string Read() { return ReadLine(); }
        private static char[] ReadChars() { return Array.ConvertAll(Read().Split(), a => a[0]); }
        private static int ReadInt() { return int.Parse(Read()); }
        private static long ReadLong() { return long.Parse(Read()); }
        private static double ReadDouble() { return double.Parse(Read()); }
        private static int[] ReadInts() { return Array.ConvertAll(Read().Split(), int.Parse); }
        private static long[] ReadLongs() { return Array.ConvertAll(Read().Split(), long.Parse); }
        private static double[] ReadDoubles() { return Array.ConvertAll(Read().Split(), double.Parse); }
    }
}
