MOD = 998244353

class ModInt:
    __slots__ = ['x']
    def __init__(self, x):
        self.x = x % MOD
    def __add__(self, other):
        return ModInt(self.x + other.x)
    def __iadd__(self, other):
        self.x = (self.x + other.x) % MOD
        return self
    def __sub__(self, other):
        return ModInt(self.x - other.x)
    def __mul__(self, other):
        return ModInt(self.x * other.x)
    def __repr__(self):
        return str(self.x)
    def __getitem__(self, i):
        return self.x[i]
    def __len__(self):
        return 1  # dummy

def karatsuba(a, b):
    n = len(a)
    m = len(b)
    if n==0 or m==0:
        return []
    if min(n,m)<=32:
        res = [ModInt(0) for _ in range(n+m-1)]
        for i in range(n):
            for j in range(m):
                res[i+j] += a[i]*b[j]
        return res
    k = max(n,m)//2
    a0,a1 = a[:k],a[k:]
    b0,b1 = b[:k],b[k:]
    z0 = karatsuba(a0,b0)
    z2 = karatsuba(a1,b1)
    a0a1 = [x+y for x,y in zip(a0 + [ModInt(0)]*(len(a1)-len(a0)), a1)]
    b0b1 = [x+y for x,y in zip(b0 + [ModInt(0)]*(len(b1)-len(b0)), b1)]
    z1 = karatsuba(a0a1, b0b1)
    # z1 - z0 - z2
    for i in range(len(z0)):
        z1[i] -= z0[i]
    for i in range(len(z2)):
        z1[i] -= z2[i]
    res = [ModInt(0)]*(n+m-1)
    for i,v in enumerate(z0): res[i] += v
    for i,v in enumerate(z1): res[i+k] += v
    for i,v in enumerate(z2): res[i+2*k] += v
    return res

def calc(a, b, f, g):
    n = len(a)
    for i in range(1,n):
        a[i] = max(a[i-1], a[i])
        b[i] = min(b[i-1]+len(g)-1, b[i])
    for i in reversed(range(1,n)):
        a[i-1] = max(a[i-1], a[i]-len(g)+1)
        b[i-1] = min(b[i-1], b[i])
    if any(x>=y for x,y in zip(a,b)):
        return []

    poly = f[:]
    for i in range(n):
        poly = karatsuba(poly, g)
        l,r = a[i], b[i]
        poly = poly[l:r]
    return poly

# ---------- main ----------
s = input().strip()
h = 1
a = []
b = []
for c in s:
    if c=='B':
        h += 1
    else:
        a.append(0)
        b.append(h)
if not a:
    print(1)
    exit()

n = len(b)
len_total = n + b[-1]
l = [0]*len_total
r = [10**9]*len_total
l[len_total-1] = b[-1]-1
for i,(aa,bb) in enumerate(zip(a,b)):
    l[i+aa] = aa
    r[i+bb] = bb

f0 = [ModInt(1)]
g = [ModInt(1), ModInt(1)]
ans_poly = calc(l,r,f0,g)
ans = ModInt(0)
for x in ans_poly:
    ans += x
print(ans)