n=int(input())
s=input()
S="Z"+s
for i in range(2,n+1):
    if (S[i-1]==S[i] or S[i-2]==S[i]) and S[i]!="?":
        print(0)
        exit()
S="ZZ"+s+"ZZ"
ans=1
mod=998244353
for i in range(2,n+2):
    if S[i].islower():
        continue
    words=set()
    count=0#注目している場所より手前の?の数
    for j in range(i-2,i+3):
        if S[j].islower():
            words.add(j)
        elif S[j]=="?" and j<i:
            count+=1
    ans*=(26-len(words)-count)
    ans%=mod
print(ans)