n = int(input())
s = input()
mod = 998244353
dp = [[0]*2 for _ in range(2)]
dp[0][0] = 1
for c in s:
    nxt = [[0]*2 for _ in range(2)]
    for i in range(2):
        for j in range(2):
            for k in range(26):
                if i==0 and ord(c)-ord('a') < k:
                    continue
                if j==1 and k==0:
                    continue
                nxt[i or ord(c)-ord('a')>k][j or k==0] += dp[i][j]%mod
    dp = nxt
print(dp[1][1]%mod)