#include<bits/stdc++.h>
#define L(i, j, k) for(int i = (j); i <= (k); ++i)
#define R(i, j, k) for(int i = (j); i >= (k); --i)
#define ll long long
#define vi vector <int>
#define sz(a) ((int) (a).size())
#define me(f, x) memset(f, x, sizeof(f))
#define uint unsig7ned int
#define ull unsigned long long 
#define i128 __int128
using namespace std;
const int N = 5000, mod = 998244353;
int qpow(int x, int y = mod - 2) {
	int res = 1;
	for(; y; x = (ll) x * x % mod, y >>= 1) if(y & 1) res = (ll) res * x % mod;
	return res;
}
int fac[N], ifac[N], inv[N];
void init(int x) {
	fac[0] = ifac[0] = inv[1] = 1;
	L(i, 2, x) inv[i] = (ll) (mod - mod / i) * inv[mod % i] % mod;
	L(i, 1, x) fac[i] = (ll) fac[i - 1] * i % mod, ifac[i] = (ll) ifac[i - 1] * inv[i] % mod;
} 
int C(int x, int y) {
	return x < y || y < 0 ? 0 : (ll) fac[x] * ifac[y] % mod * ifac[x - y] % mod;
}
inline int sgn(int x) {
	return (x & 1) ? mod - 1 : 1;
}

int n, m;
int a[N];
int b[N];

int f[N][N];
int g[N][N];
int main() {
	ios :: sync_with_stdio(false);
	cin.tie(0); cout.tie(0);
	cin >> n >> m;
	init(n + 1);
	L(i, 0, m - 1) {
		cin >> a[i];
	}
	
	int sumc = 0;
	L(i, 0, m - 1) {
		cin >> b[i];
		sumc += b[i];
	}
	
	int mul = 1;
	L(i, 0, sumc - 1) {
		mul = (ll) mul * inv[n - i] % mod;
	}
	L(i, 0, m - 1) {
		L(j, 0, b[i] - 1) {
			mul = (ll) mul * (a[i] - j) % mod;
		}
	}
	
	f[0][0] = mul;
	g[0][0] = 0;
	L(sub, 0, (1 << m) - 1) {
		int sumb = 0, qwq = 0;
		L(i, 0, m - 1) 
			if(sub >> i & 1) 
				sumb += b[i], qwq += a[i] - b[i];
		L(i, sumb, sumc - 1) {
			int kn = n - i;
			int prob = (ll) kn * inv[kn - qwq] % mod;
			int sg = (ll) prob * prob % mod;
			
			(f[sub][i + 1] += (ll) f[sub][i] * prob % mod) %= mod;
			(g[sub][i + 1] += (ll) g[sub][i] * prob % mod) %= mod;
			(g[sub][i + 1] += (ll) f[sub][i] * sg % mod) %= mod;
			
			L(p, 0, m - 1) if(!(sub >> p & 1)) {
				int c = C(i - sumb, b[p] - 1);
				(f[sub + (1 << p)][i + 1] += (ll) c * f[sub][i] % mod * prob % mod) %= mod;
				(g[sub + (1 << p)][i + 1] += (ll) c * g[sub][i] % mod * prob % mod) %= mod;
				(g[sub + (1 << p)][i + 1] += (ll) c * f[sub][i] % mod * sg % mod) %= mod;
			}
		}
	}
	cout << g[(1 << m) - 1][sumc] << '\n';
	return 0;
}
/*
3 2 
2 1
1 1


*/