using System;
using System.Collections.Generic;
using System.Linq;

namespace _672
{
    class Program
    {
        static void Main(string[] args)
        {
            Dictionary<int, List<int>> dic = new Dictionary<int, List<int>>();
            string s = Console.ReadLine() + '?';
            int count = 0;
            for (int i = 0; i < s.Length; i++)
            {
                if (!dic.ContainsKey(count)) dic[count] = new List<int>();
                dic[count].Add(i);
                if (s[i] == 'A') count++;
                if (s[i] == 'B') count--;
            }
            int ret = 0;
            foreach (var item in dic)
            {
                ret = Math.Max(ret, item.Value.Max() - item.Value.Min());
            }
            Console.WriteLine(ret);
        }
    }
}