#include<iostream>
#include<algorithm>
#include<cmath>
using namespace std;

int main()
{
	string S;
	
	cin >> S;
	
	int ans=0;
	int a[200010]={};
	int b[200010]={};
	int acnt=0;
	
	if(S[0]=='A')a[0]=1;
	if(S[0]=='B')b[0]=1;
	for(int i=1;i<S.size();i++)
	{
		//a
		a[i]=a[i-1];
		if(S[i]=='A')
		{
			if(S[i-1]=='A')a[i]++;
			else a[i]=1;
		}
		//b
		b[i]=b[i-1];
		if(S[i]=='B')
		{
			if(S[i-1]=='B')b[i]++;
			else b[i]=1;
		}
		ans=max(ans,min(a[i],b[i]	));
	}
	
	cout << ans*2 << endl;
	return 0;
}