"""

dp[i][密着][aがあるか] = ?

"""

import sys
from sys import stdin


N = int(stdin.readline())

SI = list(stdin.readline()[:-1])

S = [ord(c)-ord("a") for c in SI]

#print (S)

mod = 998244353
dp = [[0,0],[0,0]]
dp[1][0] = 1

for i in range(N):

    ndp = [[0,0],[0,0]]

    for c in range(26):

        for linka in range(2):
            for isa in range(2):
                

                if linka == 1 and S[i] < c:
                    continue
                elif isa == 1 and c == 0:
                    continue

                if c == 0:
                    if S[i] == 0:
                        ndp[1][1] += dp[linka][isa]
                    else:
                        ndp[0][1] += dp[linka][isa]
                elif linka == 1:
                    if S[i] == c:
                        ndp[1][isa] += dp[linka][isa]
                    else:
                        ndp[0][isa] += dp[linka][isa]
                else:
                    ndp[linka][isa] += dp[linka][isa]

    for x in range(2):
        for y in range(2):
            ndp[x][y] %= mod
    dp = ndp
    #print (dp)

#print (dp)
print (dp[0][1] % mod)