import sys
input = lambda :sys.stdin.readline()[:-1]
ni = lambda :int(input())
na = lambda :list(map(int,input().split()))
sys.setrecursionlimit(10**7)
yes = lambda :print("yes");Yes = lambda :print("Yes");YES = lambda : print("YES")
no = lambda :print("no");No = lambda :print("No");NO = lambda : print("NO")
#######################################################################

n = ni()
mod = 998244353
s = input()
def f(i):
    if i==n-1:
        return 0
    if i==n-2:
        if s[-1]=="?":
            return 0
        else:
            return 1
    else:
        return 2-s[i+1:i+3].count("?")
if n==1:
    if s=="?":
        print(26)
    else:
        print(1)
else:
    if s[0:2]=="??":
        ans = (26-f(0))*(25-f(1))
    elif s[0]=="?":
        ans = 25-f(0)
    elif s[1]=="?":
        ans = 25-f(1)
    elif s[0]==s[1]:
        ans = 0
    else:
        ans = 1

    for i in range(n-2):
        if s[i+2]!="?":
            if s[i]==s[i+2] or s[i+1]==s[i+2]:
                ans=0
                break
            else:
                pass
        else:
            #print(ans,f(i+2),i+2)
            ans*=24-f(i+2)
            ans%=mod
            #print(ans)
    print(ans)