using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace atcoder
{
	class Program
	{
		static int In => int.Parse(Console.ReadLine());
		static int[] Ins => Console.ReadLine().Split(' ').Select(int.Parse).ToArray();
		static void Out(bool b) => Console.WriteLine(b ? "Yes" : "No");

		static void Main(string[] args)
		{
			var str = Console.ReadLine();
			Dictionary<char, int> count = new Dictionary<char, int>();
			for (int i = 0;i < str.Length;i++)
			{
				if (count.ContainsKey(str[i])) count[str[i]]++;
				else count.Add(str[i], 1);
			}
			int ans = 0;
			foreach(var a in count)
			{
				if (a.Value % 2 == 1) ans++;
			}
			if (ans == 0) ans++;
			Console.WriteLine(ans);
			//Console.ReadLine();
		}
	}
}