#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for(int i = 0; i < int(n); i++)
#define REP(a, b, n) for(int i = a; i < b; i++)
using lint = long long;

signed main(){
	string s; cin >> s;
	int n = s.size();
	vector<int> data(n + 1, 0);
	rep(i, n){
		if(s[i] == 'A') data[i + 1] = data[i] + 1;
		else data[i + 1] = data[i] - 1;
	}
	int lim = *max_element(data.begin(), data.end());
	int ans = 0;
	for(int i = 0; i <= lim; i++){
		int a = 0, b = 0;
		rep(j, n){
			if(data[j] == i){
				a = j;
				break;
			}
		}
		for(int j = n - 1; j >= 0; j--){
			if(data[j] == i){
				b = j;
				break;
			}
		}
		ans = max(ans, b - a);
	}
	cout << ans << endl;
}