#include<bits/stdc++.h>
#define int long long
using namespace std;
int read(){
	int s = 0, f = 1;char ch = getchar();
	while(!isdigit(ch)){if(ch == '-')f = -1;ch = getchar();}
	while(isdigit(ch)){s = s * 10 + ch - '0';ch = getchar();}
	return s * f;
}
void write(int x){
    if(x < 0){putchar('-'); x = -x;}
    if(x > 9) write(x / 10);
    putchar(x % 10 + '0');
}
const int MAXN = 5e3 + 5, MR = 1e6 + 5, MOD = 1e9 + 7;
int n, k, a[MAXN], s[MAXN], f[MAXN], fac[MAXN];
signed main(){
	n = read(), k = read();
	for(int i = 1;i <= k;i ++)a[i] = read(), s[i] = s[i - 1] + a[i];
	fac[0] = 1;
	for(int i = 1;i <= n;i ++)fac[i] = fac[i - 1] * i % MOD;
	f[0] = 1;
	for(int i = 1;i <= k;i ++){
		f[i] = fac[s[i]];
		for(int j = 1;j < i;j ++){
			f[i] += (MOD - fac[s[i] - s[j]]) * f[j] % MOD;
			f[i] %= MOD;
		}
	}
	int tmp = fac[n];
	for(int i = 1;i <= k;i ++){
		tmp += (MOD - f[i] * fac[n - s[i]] % MOD) % MOD;
		tmp %= MOD;
	}
	write(tmp);
	return 0;
}