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()
N = len(S)
K = S.count("B")

def comb(x,y):
    if x < y:
        return 0
    return (((fact[x]*fact_inv[y])%MOD)*fact_inv[x-y])%MOD

ans = 1
for i in range(len(S)):
    if S[i] == "B":
        print(N-i-1,K,comb(N-i-1,K))
        ans += comb(N-i-1,K)
        ans %= MOD
        K -= 1

print(ans)