#yuki1927
n=int(input())
s=input()
ab=s.count("A")+s.count("B")
mod=998244353
res1=1
res2=1
for i in range(ab):
 res1=res1*(n-i)%mod
 res2=res2*(i+1)%mod
print(res1*pow(res2,mod-2,mod)%mod)