#include <bits/stdc++.h> #define rep(i,n) for(ll (i)=0;(i)<(n);(i)++) #define repi(i,a,b) for(ll (i)=(a);(i)<(b);(i)++) #define SIZE_OF_ARRAY(array) (sizeof(array)/sizeof(array[0])) typedef long long ll; using namespace std; int main(){ string s; cin >> s; int flag = -1; int sum = 0; int a=0,b=0; rep(i,s.size()){ if(s[i]=='A'){ a++; }else{ b++; } } while(flag<0){ for(int i=1;i<s.size();i++){ if(s[i-1]=='B' && s[i]=='A'){ s[i-1] = 'A'; s[i] = 'B'; sum++; } } string str_a = s.substr(0,a); string str_b = s.substr(a,b); int find_a = str_a.find_last_of('B'); int find_b = str_b.find_last_of('A'); if(find_a == std::string::npos){ if(find_b == std::string::npos){ flag = 1; } } } cout << sum << endl; return 0; }