using System;
using System.Collections.Generic;
using System.ComponentModel;

namespace ConsoleApp2
{
    class Program
    {
        static void Main(string[] args)
        {
            String s = Console.ReadLine();
            Int32 n = s.Length;
            Int32[] sum = new Int32[n + 1];
            for (Int32 i = 0; i < n; i++)
            {
                if (s[i] == 'A') sum[i + 1] = sum[i] + 1;
                else sum[i + 1] = sum[i] - 1;
            }

            var mp = new Dictionary<Int32, (Int32, Int32)>();
            for (Int32 i = -200000; i <= 200000; i++)
            {
                mp.Add(i,(1000,0));
            }

            Int32 ans = 0;
            for (Int32 i = 0; i < n; i++)
            {
                var (a,b) = mp[sum[i + 1]];
                if (a > i + 1) a = i + 1;
                if (b < i + 1) b = i + 1;
                mp[sum[i + 1]] = (a, b);
                ans = Math.Max(ans, b - a);
            }
            Console.WriteLine(ans);
            /*for (Int32 i = 0; i < n + 1; i++)
            {
                Console.WriteLine(sum[i]);
            }*/
        }
    }
}