#include<bits/stdc++.h>

#define int long long
using namespace std;


const long long INF = 1e5 + 10, MOD = 1e9 + 7, MOD2 = 999999937;
const long long MAXN = 1e6 + 5;

int n, h;
int k[MAXN];
int s[MAXN];
int f[MAXN];

class Solution
{
public:
    void setup(int n)
    {
        f[0] = 1;
        for (int i = 1; i <= n; i++)
        {
            f[i] = (f[i - 1] * i) % MOD;
        }
    }

    void solve()
    {
        cin >> n >> h;
        for (int i = 1; i <= h; i++)
        {
            cin >> k[i];
            s[i] = s[i - 1] + k[i];
        }

        if (s[h] == n) 
        {
            cout << 0;
            return;
        }
        setup(n);
        if (h == 0)
        {
            cout << f[n];
            return;
        }

        int m = 0;
        for (int i = 1; i < h; i++)
        {
            m += (((f[s[i]] * f[n - s[i] - 1]) % MOD) * k[i + 1]) % MOD;
        }
        m += (f[s[h]] * f[n - s[h]]) % MOD;

        cout << (f[n] + MOD - m) % MOD << '\n';

    }
};

signed main()
{
    ios::sync_with_stdio(0);
    cin.tie(0), cout.tie(0);

    Solution().solve();

    return 0;
}