MOD = 998244353
fractions = [1]
for i in range(1, 400010):
    fractions.append(fractions[-1] * i % MOD)
S = input()
C = S.count("A")
print(
    fractions[len(S)]
    * pow(fractions[C], -1, MOD)
    * pow(fractions[len(S) - C], -1, MOD)
    % MOD
)