import java.util.Scanner;
import java.util.stream.IntStream;

public class Main{
	static IntStream REPS(int v){return IntStream.range(0,v);}
	static IntStream REPS(int l,int r){return IntStream.rangeClosed(l,r);}
	static IntStream INS(int n) {return REPS(n).map(i->getInt());}
	static Scanner s=new Scanner(System.in);
	static int getInt(){return Integer.parseInt(s.next());}

	public static void main(String[]$){
		int r=0,b=0;
		char[]c=s.next().toCharArray();
		int n=c.length;
		int[]a=new int[n];
		a[n-1]=c[n-1]=='A'?1:0;
		for(int i=n-2;i>=0;--i) {
			a[i]=a[i+1]+(c[i]=='A'?1:0);
		}
		for(int i=0;i<c.length;++i) {
			if(c[i]=='B')
				r+=a[i];
		}
		System.out.println(r);
	}
}