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

int main() {
    string s;
    cin >> s;

    bool is_a = false;
    int alen = 0;
    int blen = 0;
    int result = 0;
    for(char c: s) {
        if(c == 'A') {
            if(!is_a) alen = 0;
            alen += 1;
        } else {
            if(is_a) blen = 0;
            blen += 1;
        }
        result = max(result, min(alen, blen) * 2);
        is_a = c == 'A';
    }

    cout << result << "\n";
}