#include<iostream>
#include<string>

using namespace std;

int main() {

	string str;

	cin >> str;

	int str_cout=0;
	int now=0;
	int len=0;

	if (str.size() == 1) {
		cout << len << endl;
		return 0;
	}
	else {
		for (int i = 0;i < str.size()-1;i++) {
			str_cout = 0;
			now = i;
			for (int j = i;j < str.size();j++) {
				char buf = str[j];
				if (buf == 'A')str_cout++;
				else if (buf == 'B')str_cout--;
				if (j > i && str_cout == 0) {
					int buflen = (j - now) + 1;
					if (buflen > len) {
						len = buflen;
						now = j; 
					}
				}
			}
			if (str_cout == str.size()) {
				cout << "200000" << endl;
				return 0;
			}
		}
	}

	cout << len << endl;

	return 0;
}