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

def icmb(n,r,mod):
    assert 0<=r<=n
    return (g1[r] * g1[n-r] % mod) * g2[n] % 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):
    H = [0 for i in range(N+1)]
    for i in range(1,N+1):
        H[i] = H[i-1] + inverse[i]
        H[i] %= mod

    A = [0] + A
    res = H[A[-1]-A[-2]] * N
    for i in range(1,M):
        tmp = 0
        for k in range(A[i]-A[i-1]+1):
            tmp += (cmb(N-A[i-1]-k-1,N-A[i]-1,mod) * cmb(N,A[i-1],mod) % mod) * H[k] % mod
            tmp %= mod
        tmp *= (icmb(N,A[i],mod) * icmb(A[i],A[i]-A[i-1],mod) % mod) * A[i] % mod
        res = (res + tmp) % mod
    return res % mod


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