package main

import . "fmt"

const M = 998244353

func main() {
	var s string
	Scan(&s)
	ans := 0
	cnt := 0
	for _, ch := range s {
		if ch == 'A' {
			ans = (ans + cnt + 1) % M
		} else {
			cnt = (cnt + (cnt * 2)%M + 2)%M
		}
	}
	Println(ans)
}