MOD = 998244353
n = int(input())
s = [-1 if c == '?' else ord(c) - 97 for c in input()]
for i in range(n - 1):
    if s[i] != -1 and s[i] == s[i + 1]:
        print(0)
        exit(0)
for i in range(n - 2):
    if s[i] != -1 and s[i] == s[i + 2]:
        print(0)
        exit(0)
ans = 1
for i in range(n):
    if s[i] == -1:
        t = 26 - min(2, i)
        for j in range(min(2, n - i - 1)):
            if s[i + j + 1] != -1:
                t -= 1
        ans *= t
        ans % MOD
print(ans % MOD)