n = int(input())
s = str(input())
mod = 998244353
dp = [[[0]*2 for j in range(2)] for i in range(n+1)]
dp[0][0][0] = 1
for i, c in enumerate(s):
    c = ord(c)-ord('a')
    for j in range(2):
        for k in range(2):
            for d in range(26):
                ni = i+1
                nj = j
                nk = k
                if d == 0:
                    if j == 0:
                        nj += 1
                    else:
                        continue
                if k == 0:
                    if d > c:
                        continue
                    elif d < c:
                        nk = 1
                    else:
                        pass
                dp[ni][nj][nk] += dp[i][j][k]%mod
ans = sum(dp[n][1])
if s.count('a') == 1:
    ans -= 1
print(ans%mod)