#!usr/bin/env python3
from collections import defaultdict, deque
from heapq import heappush, heappop
from itertools import permutations, accumulate
import sys
import math
import bisect
def LI(): return [int(x) for x in sys.stdin.readline().split()]
def I(): return int(sys.stdin.readline())
def IR(n):
    return [I() for _ in range(n)]
def LIR(n):
    return [LI() for _ in range(n)]

sys.setrecursionlimit(1000000)
mod = 998244353

def main():
    n = I()
    s = list(map(lambda x:ord(x)-ord("a"),input()))
    dp = [[0]*2 for _ in range(2)]
    dp[0][0] = 1
    for i in s:
        ndp = [[0]*2 for _ in range(2)]
        for j in range(2):
            x = 26 if j else i+1
            for k in range(2):
                dpjk = dp[j][k]
                if not dpjk:
                    continue
                for l in range(x):
                    nk = k+(l==0)
                    if nk > 1:
                        continue
                    nj = j|(l<i)
                    ndp[nj][nk] += dpjk
                    if ndp[nj][nk] >= mod:
                        ndp[nj][nk] -= mod
        dp = ndp
    print(dp[1][1])
    return


if __name__ == "__main__":
    main()