#include "bits/stdc++.h"
using namespace std;

vector<long long> F, RF;
long long MOD = 1000000007;

long long Calc(long long X, long long Y) {
	if (Y == 0) return 1;
	if (Y % 2 == 0) {
		long long Z = Calc(X, Y / 2);
		return (Z * Z) % MOD;
	}
	return (X * Calc(X, Y - 1)) % MOD;
}

void init(long long N) {
	F.resize(N + 1), RF.resize(N + 1);
	F[0] = F[1] = RF[0] = RF[1] = 1;
	for (int i = 2; i <= N; i++) {
		F[i] = (F[i - 1] * i) % MOD;
		RF[i] = Calc(F[i], MOD - 2);
	}
}

long long Comb(long long X, long long Y) {
	return ((F[X] * RF[X - Y]) % MOD * RF[Y]) % MOD;
}

int main() {
	long long N, K, RN;
	cin >> N >> K;
	RN = Calc(N, MOD - 2);
	init(N);
	vector<long long> A(K);
	vector<vector<long long> > DP(K + 1, vector<long long>(N + 1, 0));
	for (int i = 0; i < K; i++) cin >> A[i];
	DP[0][0] = 1;
	for (int i = 0; i < K; i++) {
		for (int j = 0; j <= N; j++) {
			for (int k = 0; k <= A[i] && j + k <= N; k++) {
				DP[i + 1][j + k] = (DP[i + 1][j + k] + (((DP[i][j] * Comb(N - j, k)) % MOD) * Comb(N - k, A[i] - k)) % MOD) % MOD;
			}
		}
	}
	cout << DP[K][N] << endl;
}