from _collections import defaultdict
n=int(input())
s=["#"]+list(input())
al=list(".#abcdefghijklmnopqrstuvwxyz")
dp=[defaultdict(int) for i in range(n+1)]
sumdp=[defaultdict(int) for i in range(n+1)]

mod=998244353
dp[0][".","#"]=1

for i in range(n+1):
    for x in al:
      for y in al:
        if i>=2 and ( x in ["#","."] or y in ["#","."]):continue
        if x==y:continue
        if s[i]=="?":
            dp[i][x,y]+=sumdp[i-1][x]
            dp[i][x,y]-=dp[i-1][y,x]
            dp[i][x,y]%=mod


        if i==n:continue
        if s[i+1]!="?":
            if s[i+1]==y or s[i+1]==x:continue
            dp[i+1][y,s[i+1]]+=dp[i][x,y]
            dp[i + 1][y, s[i + 1]]%=mod
        else:
            sumdp[i][y]+=dp[i][x,y]
            sumdp[i][y]%=mod

ans=0

for key in dp[n]:
    ans+=dp[n][key]
    ans%=mod
print(ans)