MOD = 998244353
N = int(input())
S = input()
ans = 0
f = True
for i,s in enumerate(S):
    if s == "a":
        if f:
            f = False
            continue
        else:
            break
    a = ord(s) - 97
    if f:
        ans += pow(25, N - i - 1, MOD)
        ans += (a - 1) * (N - i - 1) * pow(25, N - i - 2, MOD)
    else:
        ans += (a-1) * pow(25,N-i-1,MOD)
    ans%= MOD

print(ans)