import java.util.Arrays;
import java.util.LinkedList;
import java.util.Scanner;

public class Main {
	
	public static long MOD = 1000000007;
	
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		// めんどうなので A だけ寄せる
		final char[] ins = sc.next().toCharArray();
		
		int answer =0 ;
		
		int curr_A_index = 0;
		for(int index = 0; index < ins.length; index++){
			if(ins[index] != 'A'){ continue; }
			
			answer += (index - curr_A_index);
			curr_A_index++;
		}
		
		System.out.println(answer);
	}
}