#yuki1481
from math import *
mod=998244353
n=int(input())
s=input()
x=s.count('A')
y=s.count('B')
z=s.count('C')
if x==0 or y==0 or z==0:
 print(1)
 exit()
res=factorial(n)//(factorial(x)*factorial(y)*factorial(z))-n
print(res%mod)