import sys
input = sys.stdin.readline

def comb(n, k, mod=10**9+7):
    num = den = 1
    for i in range(k):
        num = num * (n-i) % mod
        den = den * (i+1) % mod
    return num * pow(den, mod-2, mod) % mod

N = int(input())
S = input().rstrip()
x = y = 0
for c in S:
    if c in "AB":
        x += 1
    else:
        y += 1
mod = 998244353
print(comb(x+y, y, mod))