from _collections import defaultdict
n=int(input())
s=["#"]+list(input())
dic={}
dic["#"]=-1
dic["."]=-2
dic["?"]=-34
al=list(".#abcdefghijklmnopqrstuvwxyz")

for x in al:dic[x]=ord(x)-97
for i in range(n+1):
    s[i]=dic[s[i]]


dp=[[[0]*33 for _ in range(33)] for i in range(n+2)]
sumdp=[[0]*(33) for i in range(n+1)]

mod=998244353
dp[0][-2][-1]=1

for i in range(n+1):
    for x in range(-2,26):
      for y in range(-2,26):
        if i>=2 and ( x<0 or y<0):continue
        if x==y:continue
        if s[i]==-34:
            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]!=-34:
            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 x in range(26):
    for y in range(26):
        ans+=dp[n][x][y]
        ans%=mod

print(ans)