n = int(input())
s = input()
F = 0
for lst in ["ABC","BCA","CAB"]:
    v = 0
    for i in lst:
        v = s.find(i,v)+1
        if v==0:
            break
    F = max(F,v)
if F==0:
    print(1)
    exit()
from math import factorial as f
r = f(len(s))
for i in "ABC": r //= f(s.count(i))
print((r-len(s))%998244353)