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=[defaultdict(int) for i in range(n+1)]
sumdp=[defaultdict(int) 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 key in dp[n]:
    ans+=dp[n][key]
    ans%=mod
print(ans)