def cmb(n, r, mod):#コンビネーションの高速計算　
    if ( r<0 or r>n ):
        return 0
    r = min(r, n-r)
    return (g1[n] * g2[r] % mod) * g2[n-r] % mod

mod = 998244353#出力の制限
N = 2*10**5
g1 = [1]*(N+1) # 元テーブル
g2 = [1]*(N+1) #逆元テーブル
inverse = [1]*(N+1) #逆元テーブル計算用テーブル

for i in range( 2, N + 1 ):
    g1[i]=( ( g1[i-1] * i ) % mod )
    inverse[i]=( ( -inverse[mod % i] * (mod//i) ) % mod )
    g2[i]=( (g2[i-1] * inverse[i]) % mod )
inverse[0]=0

import sys,random,bisect
from collections import deque,defaultdict
from heapq import heapify,heappop,heappush
from itertools import permutations
from math import log,gcd

input = lambda :sys.stdin.readline().rstrip()
mi = lambda :map(int,input().split())
li = lambda :list(mi())

def solve(N,M,A):
    A = [0] + A

    B = [0 for i in range(N+1)]
    for i in range(M+1):
        for j in range(A[i]+1,N+1):
            B[j] = i

    dp_res = [[0 for j in range(N+2)] for i in range(N+1)]
    dp_det_p = [[0 for j in range(N+2)] for i in range(N+1)]

    for i in range(1,N+1):
        n = B[i]
        for j in range(A[n],-1,-1):
            if i!=A[n]+1:
                dp_res[i][j] = (A[n+1] + (A[n]-j) * dp_res[i][j+1] + (i-A[n]) * dp_res[i-1][j]) % mod
                dp_res[i][j] *= inverse[i-j]
                dp_res[i][j] %= mod
            else:
                dp_res[i][j] = (A[n+1] + (A[n]-j) * dp_res[i][j+1] + dp_det_p[i-1][j]) % mod
                dp_res[i][j] *= inverse[i-j]
                dp_res[i][j] %= mod

        if i==A[n+1]:
            for j in range(i+1):
                inv = (g2[i] * g1[j] % mod) * g1[i-j] % mod
                for k in range(i-A[n]):
                    dp_det_p[i][j] += ((cmb(i-A[n],k,mod) * cmb(A[n],j-k,mod) % mod) * dp_res[i-k][j-k] % mod) * inv % mod
                    dp_det_p[i][j] %= mod
                dp_det_p[i][j] += (cmb(A[n],j-(i-A[n]),mod) * dp_det_p[A[n]][j-(i-A[n])] % mod) * inv % mod
                dp_det_p[i][j] %= mod

    return dp_res[N][0]

N,M = mi()
A = li()
print(solve(N,M,A) % mod)