def solve_A(n, s):
    dp = [[[0] * 2 for _ in range(2)] for _ in range(n + 5)]
    dp[0][0][0] = 1
    mod = 998244353
    #dp[i][aflag][smallflag]
    for i in range(n):
        #aを除くアルファベット25文字の遷移
        for j in range(25):
            dp[i + 1][True][True] += dp[i][True][True]
            dp[i + 1][False][True] += dp[i][False][True]

        #aがi文字目で初めて含まれるものの遷移
        dp[i + 1][True][True] += dp[i][False][True]

        now = ord(s[i]) - ord('a')

        #smallflagがFalseからTrueへ遷移する
        for j in range(now):
            if j == 0:
                dp[i + 1][True][True] += dp[i][False][False]
            else:
                dp[i + 1][True][True] += dp[i][True][False]
                dp[i + 1][False][True] += dp[i][False][False]
        
        #smallflagのFalseからFalseへの遷移
        if now == 0:
            dp[i + 1][True][False] += dp[i][False][False]
        else:
            dp[i + 1][False][False] += dp[i][False][False]
            dp[i + 1][True][False] += dp[i][True][False]
        
        #modを取る
        for j in range(2):
            for k in range(2):
                dp[i + 1][j][k] %= mod
    #答えはdp[n][True][True]
    return dp[n][True][True]


n = int(input())
s = input()
print(solve_A(n, s))