mod = 998244353
eps = 10**-9


def main():
    import sys
    input = sys.stdin.readline

    N = int(input())
    S = input().rstrip('\n')

    dp00 = [0] * (N+1)
    dp01 = [0] * (N+1)
    dp10 = [0] * (N+1)
    dp11 = [0] * (N+1)
    dp00[0] = 1
    for i, s in enumerate(S):
        if s != "a":
            dp00[i+1] = dp00[i]
        if s == "a":
            dp01[i+1] = dp00[i]
        else:
            dp01[i+1] = dp01[i]
        j = ord(s) - 97
        dp10[i+1] = (dp10[i] * 25 + dp00[i] * max(0, j-1))%mod
        if s != "a":
            dp11[i+1] = (dp11[i] * 25 + dp00[i] + dp01[i] * max(0, j-1) + dp10[i])%mod
        else:
            dp11[i + 1] = (dp11[i] * 25 + dp10[i]) % mod
    print(dp11[-1])


if __name__ == '__main__':
    main()