import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    String s = sc.next();
    int n = 0;
    int sum = 0;
    for(int i = 0; i < s.length(); i++) {
      if(s.charAt(i) == 'A') {
        n++;
        sum += i;      
      }
    }
    int ans = sum - (n * (n - 1)) / 2;
    System.out.println(ans);
  }
}