#include <iostream>
#include <string>
#include <vector>
#include <queue>
#include <deque>
#include <algorithm>
#include <set>
#include <map>
#include <bitset>
#include <cmath>
#include <functional>
#include <iomanip>
#define vll vector<ll>
#define vvvl vector<vvl>
#define vvl vector<vector<ll>>
#define VV(a, b, c, d) vector<vector<d>>(a, vector<d>(b, c))
#define VVV(a, b, c, d) vector<vvl>(a, vvl(b, vll (c, d)));
#define re(c, b) for(ll c=0;c<b;c++)
#define rep(a,b,c) for(ll a=b;a<c;a++)
#define all(obj) (obj).begin(), (obj).end()
typedef long long int ll;
typedef long double ld;
using namespace std;

void get(vll &a){re(i,a.size()) scanf("%lld",&a[i]);}
void get(vvl &a){re(i,a.size()) re(j,a[0].size()) scanf("%lld",&a[i][j]);}
void print(vll &a){re(i,a.size()) cout<<a[i]<<(i==a.size()-1?"\n":" ");}
void print(vvl &a){re(i,a.size()) re(j,a[0].size())cout<<a[i][j]<<(j==a[0].size()-1?"\n":" ");}

struct BIT{
  ll M=1;
  vector<ll> dat;
  BIT(ll N){
    while(N>M) M*=2;
    dat.resize(M*2-1, 0);
  }
  void update(ll x, ll k){
    for(int i=k+1;i<=M;i+=(i&(-i))){
      dat[i] += x;
    }
  }
  ll sum(ll r){
    ll ret = 0;
    for(int k=r;k>0;k-=(k&(-k))) ret += dat[k];
    return ret;
  }

  ll query(ll l, ll r){
    return sum(r) - sum(l);
  }
};
int main(int argc, char const *argv[]) {
  string s;std::cin >> s;
  BIT seg(s.size()+1);
  ll ans = 0;
  for(int i=0;i<s.size();i++){
    if(s[i]=='A'){
      ans += seg.query(0, i);
    }else{
      seg.update(1, i);
    }
  }
  std::cout << ans << '\n';
}