N = int(input())
S = list(input())
store = set()
ans = 0
cnt = 0
mod = 998244353
def change(s):
    return ord(s) - ord('a') + 1
for i in  range(N):
    store.add(S[i])
    if S[i] == 'a':
        cnt += 1
    if cnt >= 2:
        continue
    if 'a' in store:
        tmp = (change(S[i]) -2) * pow(25,N-1-i,mod)
        if tmp > 0:
            ans += tmp
            ans %= mod
    else:
        if N -1 - i > 0:
            tmp = (change(S[i]) -2) * pow(25,N-1-i-1,mod) * (N-1-i)
            if tmp > 0:
                ans += tmp
                ans %= mod
        ans += pow(25,N-1-i,mod)
        ans %= mod
print(ans)