import sys
input = sys.stdin.readline
from collections import *

N = int(input())
S = input()[:-1]
dp = [[[0]*2 for _ in range(2)] for _ in range(N+1)]
dp[0][0][0] = 1
MOD = 998244353

for i in range(N):
    d = ord(S[i])-ord('a')
    
    for j in range(2):
        for k in range(2):
            for c in range(26 if j else d+1):
                if k==1 and c==0:
                    continue
                
                nj = j|(c<d)
                nk = k+(c==0)
                dp[i+1][nj][nk] += dp[i][j][k]
                dp[i+1][nj][nk] %= MOD

print(dp[N][1][1])