using System;

public class Program
{
    private string S;

    private int L = 1 << 26;
    private int[] Dp;

    public void Solve()
    {
        var sc = new Scanner();
        S = sc.Next();

        // 
        Dp = new int[L];
        for (int i = 0; i < L; i++)
        {
            Dp[i] = 200000;
        }

        Dp[0] = 0;

        int state = 0;

        foreach (char c in S)
        {
            state ^= 1 << (c - 'a');
            int ans = Dp[state];
            for (char cc = 'a'; cc <= 'z'; cc++)
            {
                int tmp = state ^ (1 << (cc - 'a'));
                ans = Math.Min(ans, Dp[tmp] + 1);
            }

            Dp[state] = ans;

            // Console.WriteLine($"{Convert.ToString(state, 2)} {Dp[state]}");
        }

        Console.WriteLine(Dp[state]);
    }

    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
}