## https://yukicoder.me/problems/no/1740

MOD = 998244353

def main():
    N = int(input())
    S = input()

    answer = 0
    has_one_a = False
    for i in range(N - 1):
        s = S[i]
        if s >= "b":
            if not has_one_a:
                answer += pow(25, N - 1 - i, MOD)
                answer %= MOD
        if s >= "c":
            v = ord(s) - 1 - ord("a")
            if not has_one_a:
                ans = ((N - 1 - i) * pow(25, N - 2 - i, MOD)) % MOD
                answer += (v * ans) % MOD
                answer %= MOD
            else:
                answer += pow(25, N - 1 - i, MOD)
                answer %= MOD
        
        if s == "a":
            if not has_one_a:
                has_one_a = True
            else:
                print(answer)
                return
    
    # 最後の一つについて
    s = ord(S[-1]) - ord("a")
    for t in range(s):
        if t == 0 and not has_one_a:
            answer += 1
            answer %= MOD
        if t > 0 and has_one_a:
            answer += 1
            answer %= MOD
    print(answer)

    



if __name__ == "__main__":
    main()