MOD = 998244353
U = 10**6
fact = [1]
for i in range(1,U+1):
  fact.append((fact[-1]*i)%MOD)
fact_inv = [-1]*(U+1)
fact_inv[U] = pow(fact[U],-1,MOD)
for i in range(U-1,-1,-1):
  fact_inv[i] = fact_inv[i+1]*(i+1)%MOD

#print(fact)
#print(fact_inv)

S = input()

a = S.count("A")
b = S.count("B")

ans = (((fact[a+b] * fact_inv[a]) % MOD ) * fact_inv[b])%MOD
print(ans)