import sys
INF = float('inf')
#10**20,2**63,float('inf')
MOD = 10**9 + 7
MOD2 = 998244353
#from collections import defaultdict
def solve():
    def II(): return int(sys.stdin.readline())
    def LI(): return list(map(int, sys.stdin.readline().split()))
    def LC(): return list(input())
    def IC(): return [int(c) for c in input()]
    def MI(): return map(int, sys.stdin.readline().split())
    N = II()
    S = LC()
    Alpha = {}
    for i in range(97, 123):
        Alpha[chr(i)] = i - 97
        Alpha[i-97] = chr(i)
    DP = [[[0]*26 for _ in range(26)] for _ in range(N+10)]
    if S[0] == "?":
        for i in range(26):
            DP[1][0][i] = 1
    else:
        DP[1][0][Alpha[S[0]]] = 1
    if N == 1:
        print(sum(DP[1][0]))
        exit()

    if S[1] == "?":
        for i in range(26):
            for j in range(26):
                if i == j:continue
                DP[2][i][j] += DP[1][0][i]
    else:
        for i in range(26):
            if i == Alpha[S[1]]:continue
            DP[2][i][Alpha[S[1]]] += DP[1][0][i]
    if N == 2:
        Ans = 0
        for i in range(26):
            Ans += sum(DP[2][i])
        print(Ans)
        exit()
    for n in range(2,N):
        for i in range(26):
            for j in range(26):
                if S[n] == "?":
                    for k in range(26):
                        if i == k or j == k:continue
                        DP[n + 1][j][k] += DP[n][i][j]
                        DP[n + 1][j][k] %= MOD2
                else:
                    if i == Alpha[S[n]] or j == Alpha[S[n]]:continue
                    DP[n+1][j][Alpha[S[n]]] += DP[n][i][j]
                    DP[n + 1][j][Alpha[S[n]]] %= MOD2
        #print(DP[n+1])
    Ans = 0
    for i in range(26):
        for j in range(26):
            Ans += DP[N][i][j]
            Ans %= MOD2
    print(Ans % MOD2)
    return
solve()
#sys.setrecursionlimit(10 ** 6)#再帰関数ではコメントにしないこと！！