#include <algorithm>
#include <cmath>
#include <cstring>
#include <deque>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <string>
#include <unordered_map>
#include <vector>

using namespace std;
using ll = long long;

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);

    string s;
    cin >> s;
    int ans = 0;

    for (int i = 0; i < s.size(); i++) {
        int a = 0;
        int b = 0;
        s[i] == 'A' ? a++ : b++;
        for (int j = i + 1; j < s.size(); j++) {
            s[j] == 'A' ? a++ : b++;
            if (a == b) {
                ans = max(ans, a + b);
            }
        }
    }

    cout << ans << endl;

    return 0;
}