n=int(input())
s=input()
cnt=1
Mod=998244353
for i in range(n):
  if s[i]=='?':
    t=set()
    u=0
    for j in [-2,-1,1,2]:
      if i+j>=0 and j<0:
        if s[i+j]=='?':
          u+=1
        else:
          t.add(s[i+j])
      elif 0<=i+j<n and s[i+j]!='?':
        t.add(s[i+j])
    cnt*=26-len(t)-u
  else:
    if i+1<n and s[i]==s[i+1]:
      cnt=0
    if i+2<n and s[i]==s[i+2]:
      cnt=0
  cnt%=Mod
print(cnt)