from itertools import product

def count():
    n = int(input())
    a = input()
    mod = 998244353
    #配列は末から
    dp=[[[0] * 3 for k in range(2)] for l in range(n+1)]
    dp[0][0][0] = 1

    #条件に合わせてDP
    for i, less, cnta in product(range(n), (0,1), range(3)):
        max_d = 25 if less else int(ord(a[i])-97)
        for d in range(max_d+1):
            less_ = less or d < max_d
            cnta_ = min(2, cnta + int(d==0))
            dp[i + 1][less_][cnta_] = (dp[i][less][cnta]+dp[i + 1][less_][cnta_])%mod
    
    #合致するものを合算
    ret = dp[n][1][1]
    return ret

print(count())