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

namespace AtCorder
{
	public class Program
	{
		static void Main(string[] args)
		{
			C();
		}

		public static void C()
		{
			Scanner cin = new Scanner();
			string s = cin.Next();
			List<int> v = new List<int>();
			for (int n = 0; n < s.Length; ++n) {
				v.Add(s[n] == '0' ? 0 : 1);
			}

			int count = Hoge(s, 0);
			Console.WriteLine(count);
		}

		public static int Hoge(string s, int count)
		{
			int n = s.Length - 1;
			if (n <= 0) {
				return count;
			}

			int maxCount = count;
			Parallel.For(0, n, m => {
				if (s[m] != s[m + 1]) {
					int count2 = count + 2;
					string s2 = s.Remove(m, 2);
					int count3 = Hoge(s2, count2);

					if (count3 > maxCount) {
						maxCount = count3;
					}
				}
			});

			return maxCount;
		}

		public static int Piyo(List<int> s, int count)
		{
			int n = s.Count - 1;
			if (n <= 0) {
				return count;
			}

			int maxCount = count;
			for (int m = 0; m < n; ++m) {
				var s2 = new List<int>(s);
				if (s2[m] != s2[m + 1]) {
					int count2 = count + 2;
					s2.RemoveRange(m, 2);
					int count3 = Piyo(s2, count2);

					if (count3 > maxCount) {
						maxCount = count3;
					}
				}
			}

			return maxCount;
		}

		
	}

	public class Scanner
	{
		string[] s;
		int i;

		char[] cs = new char[] { ' ' };

		public Scanner()
		{
			s = new string[0];
			i = 0;
		}

		public string Next()
		{
			if (i < s.Length) return s[i++];
			string st = Console.ReadLine();
			while (st == "") st = Console.ReadLine();
			s = st.Split(cs, StringSplitOptions.RemoveEmptyEntries);
			if (s.Length == 0) return Next();
			i = 0;
			return s[i++];
		}

		public int NextInt()
		{
			return int.Parse(Next());
		}
		public int[] ArrayInt(int N, int add = 0)
		{
			int[] Array = new int[N];
			for (int i = 0; i < N; i++) {
				Array[i] = NextInt() + add;
			}
			return Array;
		}

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

		public long[] ArrayLong(int N, long add = 0)
		{
			long[] Array = new long[N];
			for (int i = 0; i < N; i++) {
				Array[i] = NextLong() + add;
			}
			return Array;
		}

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


		public double[] ArrayDouble(int N, double add = 0)
		{
			double[] Array = new double[N];
			for (int i = 0; i < N; i++) {
				Array[i] = NextDouble() + add;
			}
			return Array;
		}
	}
}
