N = int(input())
S = list(input())
mod = 998244353
for i in range(N):
    S[i] = ord(S[i]) - ord("a")

dp = [[[0] * 2 for i in range(2)] for i in range(N + 1)]
dp[0][0][0] = 1
for i in range(N):
    for a in range(2):
        for b in range(2):
            for n in range(26):
                if a == 0:
                    if n > S[i]:
                        continue
                    if n == S[i]:
                        na = 0
                    else:
                        na = 1
                else:
                    na = 1

                if b == 1:
                    if n == 0:
                        continue
                    nb = 1
                else:
                    if n == 0:
                        nb = 1
                    else:
                        nb = 0

                dp[i + 1][na][nb] += dp[i][a][b]
                dp[i + 1][na][nb] %= mod

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