import sys

# sys.setrecursionlimit(200005)
int1 = lambda x: int(x)-1
p2D = lambda x: print(*x, sep="\n")
def II(): return int(sys.stdin.readline())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def SI(): return sys.stdin.readline().rstrip()
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
# inf = 18446744073709551615
inf = 4294967295
# md = 10**9+7
md = 998244353

n = II()
aa = [ord(c)-97 for c in SI()]

# dp[見た個数][aを使った][未満確定]
dp = [[[0]*2 for _ in range(2)] for _ in range(n+1)]
dp[0][0][0] = 1

def add(i, j, k, val):
    dp[i][j][k] = (dp[i][j][k]+val)%md

for i, a in enumerate(aa):
    for j in range(2):
        for k in range(2):
            pre = dp[i][j][k]
            if pre == 0: continue
            for c in range(26):
                nj = j
                nk = k
                if j and c == 0: continue
                if c == 0: nj = 1
                if k == 0 and c > a: continue
                if c < a: nk = 1
                add(i+1, nj, nk, pre)

print(dp[-1][1][1])