n = int(input())
s = input()
p = 998244353
alptonum = {"a":1,"b":2,"c":3,"d":4,"e":5,"f":6,"g":7,"h":8,"i":9,"j":10,"k":11,"l":12,"m":13,"n":14,"o":15,"p":16,"q":17,"r":18,"s":19,"t":20,"u":21,"v":22,"w":23,"x":24,"y":25,"z":26}

dp = [[0 for i in range(2)] for j in range(n+1)]
dp2 = [[0 for i in range(2)] for j in range(n+1)]
dp2[0][0] = 1

for i in range(n):
    kari = alptonum[s[i]]
    if kari != 1:
        dp[i+1][0] = (dp[i][0] * 25 + dp2[i][0] * (kari - 2)) % p
        dp[i+1][1] = (dp[i][0] + dp2[i][0] + dp[i][1] * 25 + dp2[i][1] * (kari - 2)) % p
        dp2[i+1][0] = dp2[i][0]
        dp2[i+1][1] = dp2[i][1]
    else:
        dp[i+1][0] = (dp[i][0] * 25) % p
        dp[i+1][1] = (dp[i][0] + dp[i][1] * 25) % p
        dp2[i+1][1] = dp2[i][0]

ans = (dp[n][1]) % p
print("{}".format(ans))