#include <bits/stdc++.h>
using namespace std;
int main(){
	ios::sync_with_stdio(0);
	cin.tie(0); cout.tie(0);
	int N, K; cin >> N >> K; 
	long long mod = 1000000007; 
	long long B[1010][1010] = {}; 
	B[0][0] = 1; 
	for(int i = 0; i < 1005; i++){
		for(int j = 0; j <= i; j++){
			B[i+1][j] += B[i][j];
			B[i+1][j+1] += B[i][j];
			if(B[i+1][j] >= mod) B[i+1][j] -= mod;
			if(B[i+1][j+1] >= mod) B[i+1][j+1] -= mod;
		}
	}
	long long dp[21][1010] = {}; // dp[i日目まで終えて][スペシャルクッキーをj個配布済]
	dp[0][0] = 1; 
	int A[21] = {}; 
	for(int i = 1; i <= K; i++) cin >> A[i]; 
	for(int i = 1; i <= K; i++){
		for(int j = 0; j <= N; j++){
			if(dp[i-1][j] == 0) continue; 
			for(int k = j; k <= min(N, j + A[i]); k++){
				long long tmp = B[N-j][k-j] * B[N-k+j][A[i]-k+j] % mod; 
				tmp *= dp[i-1][j]; tmp %= mod;
				dp[i][k] += tmp; 
				if(dp[i][k] >= mod) dp[i][k] -= mod; 
			}
		}
	}
	cout << dp[K][N] << "\n"; 
}