using System;
using System.Collections.Generic;

public class Program
{
    private string S;
    private int N;

    public void Solve()
    {
        var sc = new Scanner();
        S = sc.Next();
        N = S.Length;
        int[] state = new int[N + 1];
        for (int i = 0; i < N; i++)
        {
            state[i + 1] = state[i] ^ ToInt(S[i]);
        }

        var map = new Dictionary<int, int>();

        for (int i = 0; i <= N; i++)
        {
            map[state[i]] = i;
        }

        var dp = new int[N + 1];

        for (int i = 1; i <= N; i++)
        {
            dp[i] = int.MaxValue;
        }

        for (int i = 0; i <= N; i++)
        {
            if (dp[i] != int.MaxValue)
            {
                int o;
                {
                    if (map.TryGetValue(state[i], out o))
                    {
                        if (o > i)
                            dp[o] = Math.Min(dp[o], dp[i] + 1);
                    }
                }
                for (char c = 'a'; c <= 'z'; c++)
                {
                    int next = state[i] ^ ToInt(c);
                    if (map.TryGetValue(next, out o))
                    {
                        if (o > i)
                            dp[o] = Math.Min(dp[o], dp[i] + 1);
                    }
                }
            }
        }

        Console.WriteLine(dp[N]);
    }

    private int ToInt(char c)
    {
        int n = c - 'a';
        return 1 << n;
    }

    public static void Main(string[] args)
    {
        new Program().Solve();
    }
}

class Scanner
{
    public Scanner()
    {
        _pos = 0;
        _line = new string[0];
    }

    const char Separator = ' ';
    private int _pos;
    private string[] _line;

    #region スペース区切りで取得

    public string Next()
    {
        if (_pos >= _line.Length)
        {
            _line = Console.ReadLine().Split(Separator);
            _pos = 0;
        }

        return _line[_pos++];
    }

    public int NextInt()
    {
        return int.Parse(Next());
    }

    public long NextLong()
    {
        return long.Parse(Next());
    }

    public double NextDouble()
    {
        return double.Parse(Next());
    }

    #endregion

    #region 型変換

    private int[] ToIntArray(string[] array)
    {
        var result = new int[array.Length];
        for (int i = 0; i < array.Length; i++)
        {
            result[i] = int.Parse(array[i]);
        }

        return result;
    }

    private long[] ToLongArray(string[] array)
    {
        var result = new long[array.Length];
        for (int i = 0; i < array.Length; i++)
        {
            result[i] = long.Parse(array[i]);
        }

        return result;
    }

    private double[] ToDoubleArray(string[] array)
    {
        var result = new double[array.Length];
        for (int i = 0; i < array.Length; i++)
        {
            result[i] = double.Parse(array[i]);
        }

        return result;
    }

    #endregion

    #region 配列取得

    public string[] Array()
    {
        if (_pos >= _line.Length)
            _line = Console.ReadLine().Split(Separator);

        _pos = _line.Length;
        return _line;
    }

    public int[] IntArray()
    {
        return ToIntArray(Array());
    }

    public long[] LongArray()
    {
        return ToLongArray(Array());
    }

    public double[] DoubleArray()
    {
        return ToDoubleArray(Array());
    }

    #endregion
}