mod=998244353
def inv(a):
    rem,ans=mod-2,1
    while rem:
        if rem%2:
            ans=(ans*a)%mod
        a=(a*a)%mod
        rem//=2
    return ans
N=int(input())
S=input()
C=sum([i in ['A','B'] for i in S])
ans=[1,1]
for i in range(1,C+1):
    ans[0]=(ans[0]*i)%mod
    ans[1]=(ans[1]*(i+len(S)-C))%mod
print((inv(ans[0])*ans[1])%mod)