n = int(input())
S = input()
L = [ord(s)-ord("a") for s in S]
mod = 998244353

dp = [[0,0],[0,0]]
dp[1][0] = 1

for l in L:
    ndp = [[0,0],[0,0]]
    for i in range(26):
        if i:
            ndp[0][0] += dp[0][0]
            ndp[0][0] %= mod
            ndp[0][1] += dp[0][1]
            ndp[0][1] %= mod

        else:
            ndp[0][1] += dp[0][0]
            ndp[0][1] %= mod

        if i < l:
            if i:
                ndp[0][0] += dp[1][0]
                ndp[0][0] %= mod
                ndp[0][1] += dp[1][1]
                ndp[0][1] %= mod

            else:
                ndp[0][1] += dp[1][0]
                ndp[0][1] %= mod
        
        elif i == l:
            if i:
                ndp[1][0] += dp[1][0]
                ndp[1][0] %= mod
                ndp[1][1] += dp[1][1]
                ndp[1][1] %= mod

            else:
                ndp[1][1] += dp[1][0]
                ndp[1][1] %= mod
    dp = ndp
print(dp[0][1])