#include <iostream>
#include <string>

int main() {
    long long A = 0, C = 0, a = 0, n = 0;
    char L = 'A';
    std::string S;
    
    std::cin >> S; // Assuming the first input is not used as per the Python code
    
    for (char s : S) {
        if (s == L) {
            A += 1;
        } else {
            C += 1;
            n += A;
        }
    }
    
    long long c = C;
    long long m = n;
    for (char s : S) {
        if (s < L) {
            n += c - 1 - a;
            a += 1;
            c -= 1;
        }
        c -= s > L;
        a += s == L;
        m = std::max(n, m);
    }
    
    std::cout << m << std::endl;
    
    return 0;
}