import sys
sys.setrecursionlimit(10**7)
from functools import cache
MOD=998244353
@cache
def factorial(d):
    if d == 0 or d == 1:
        return 1
    else:
        return (d * factorial(d - 1))

N=int(input())
n=N//2
S=input()
if S[0]!=S[1]:
  type=1
else:
  type=0
if type==1:
  ans = 1
  for i in range(n):
    ans=(ans*2)%MOD
else:
  ans = 0
  for r in range(0, n+1):
    x=factorial(n)//factorial(n-r)//factorial(r)
    ans = (ans + x*x)%MOD
print(ans)