#include <cmath>
#include <vector>
#include <list>
#include <map>
#include <set>
#include <functional>
#include <queue>
#include <iostream>
#include <string.h>
#include <iomanip>
#include <algorithm>
#include <functional>
#include <cstdint>
#include <climits>
#include <unordered_set>
#include <sstream>
#include <stack>

using namespace std;

typedef long long int ll;
typedef pair<int,int> pii;
typedef tuple<ll,ll,ll> t3;

using namespace std;

map<char, set<char>> g;
map<char, int> color;

int main()
{
    string s;
    cin >> s;
    int a = 0;
    vector<char> v;
    const char A = 'A';
    const char B = 'B';
    int n = (int)s.length();
    for(int i = 0;i < n;i++)
    {
        v.push_back(s[i]);
        if(s[i] == A)
        {
            a++;
        }
    }
    int count = 0;
    for(int i = 0;i < a;i++)
    {
        if(v[i] != A)
        {
            for(int j = i + 1;j < n;j++)
            {
                if(v[j] == A)
                {
                    count += j-i;
                    v[i] = A;
                    v[j] = B;
                    break;
                }
            }
        }
    }
    cout << count << endl;
    return 0;
}