MOD = 998244353
N = int(input())
A = list(range(N+1))
A[0] = 1
for i in range(3,N+1):
    A[i] = (A[i-1]*i)%MOD
B = [1]*(N+1)
B[N] = pow(A[N],MOD-2,MOD)
for i in range(N-1,0,-1):
    B[i] = (B[i+1]*(i+1))%MOD
def comb(n,k):
    if k>n or k<0:
        return 0
    return (A[n]*B[k]*B[n-k])%MOD
S = input().strip()
K = 0
for s in S:
    if s in ["A","B"]:
        K += 1
print(comb(N,K))