MOD = 998244353

s = input().strip()

h = 1
segments = []
for c in s:
    if c=='B':
        h += 1
    else:
        segments.append(h)

if not segments:
    print(1)
    exit()

ans = 1
prev_h = 1
for h in segments:
    # Har bir A: oxirgi balandlikdan h gacha bo'lgan barcha variantlar
    ans = ans * h % MOD

print(ans)