#include <bits/stdc++.h>
using namespace std;
#include <atcoder/all>

using mint = atcoder::modint998244353;
#pragma region Math ACL Combination

const int CombMAX = 3000000;
std::vector<mint> fac(CombMAX + 1), finv(CombMAX + 1), inv(CombMAX + 1);

struct Combinationinit {
	Combinationinit() {
		const int MOD = mint::mod();
		fac[0] = fac[1] = 1;
		finv[0] = finv[1] = 1;
		inv[1] = 1;
		for(int i = 2; i <= CombMAX; i++) {
			fac[i] = fac[i - 1] * i;
			inv[i] = (mint)MOD - inv[MOD % i] * (MOD / i);
			finv[i] = finv[i - 1] * inv[i];
		}
	}
} Combinationinit_;

//nCk
mint COM(int n, int k) {
	if(n < k or n < 0 or k < 0) return 0;
	assert(n <= CombMAX);
	return fac[n] * finv[k] * finv[n - k];
}

mint bigCOM(int n, int k) {
	if(n < k or n < 0 or k < 0) return 0;
	mint res = finv[k];
	for(int i = 1; i <= k; ++i)
		res *= (n + 1 - i);
	return res;
}

//nPk
mint PER(int n, int k) {
	if(n < k or n < 0 or k < 0) return 0;
	assert(n <= CombMAX);
	return fac[n] * finv[n - k];
}

//nHk
mint HOM(int n, int k) {
	assert(n <= CombMAX);
	return COM(n + k - 1, k);
};
#pragma endregion

int n, m, a[2000];
int main() {
	scanf("%d%d", &n, &m);
	for(int i = 0; i < m; i++) scanf("%d", &a[i]);
	vector dp(m + 1, vector(0, vector(0, mint(0))));
	vector sub(m + 1, vector(n + 1, mint(0)));
	for(int k = 0; k < m; k++) {
		int len_i = (k ? a[k] - a[k - 1] : a[0]);
		int len_j = (k ? a[k - 1] : 0);
		dp[k].assign(len_i + 1, vector(len_j + 1, mint(0)));
		
		for(int i = 0; i <= len_i; i++) {
			for(int j = 0; j <= len_j; j++) {
				if(!i and !j) continue;
				auto &now = dp[k][i][j];
				now = (mint)a[k];
				if(j) now += dp[k][i][j - 1] * j;
				if(i >= 2) now += dp[k][i - 1][j] * i;
				if(i == 1 and k) {
					now += sub[k - 1][j] * i;
				}
				now *= inv[i + j];
			}
		}
		
		for(int i = 0; i <= a[k]; i++) {
			if(k) {
				sub[k][i] = sub[k - 1][i] * COM(a[k - 1], i) / COM(a[k], i);
				for(int z = 1; z <= a[k] - a[k - 1] and i - z >= 0; z++)
					sub[k][i] += dp[k][z][i - z] * COM(a[k] - a[k - 1], z) * COM(a[k - 1], i - z) / COM(a[k], i);
			} else if(i)
				sub[k][i] = sub[k][i - 1] + (mint)a[0] / i;
		}
	}
	cout << dp[m - 1][a[m - 1] - a[m - 2]][a[m - 2]].val() << endl;
}