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

typedef long long ll;
const ll mod = 1e9 + 7;

ll fpow(ll a, ll b)
{
    ll ans = 1;
    while (b)
    {
        if (b & 1) ans = ans * a % mod;
        a = a * a % mod;
        b >>= 1;
    }
    return ans;
}

int c[505];
ll fac, ifac[505];
ll f[505][505], pre[505][505];

inline void chkadd(ll &x, ll y) { ((x += y) >= mod) && (x -= mod); (x < 0) && (x += mod); }

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);

    int n, m; cin >> n >> m;
    for (int i = 1; i <= m; i++) cin >> c[i];
    fac = 1; for (int i = 1; i <= n; i++) (fac *= i) %= mod;
    ifac[n] = fpow(fac, mod - 2); for (int i = n - 1; ~i; i--) ifac[i] = ifac[i + 1] * (i + 1) % mod;

    f[0][0] = 1;
    for (int i = 0; i <= n; i++)
    {
        for (int j = 0; j <= m; j++) pre[i][j] = f[i][j];
        for (int k = i + 1; k <= n; k++)
        {
            pre[k][0] = pre[k - 1][0];
            for (int j = 1; j <= m; j++) chkadd(pre[k][j] = pre[k - 1][j], (k >= c[j] ? pre[k - c[j]][j - 1] : 0) - pre[k - 1][j - 1]);
            for (int j = 1; j <= m; j++) chkadd(f[k][j], (pre[k - 1][j - 1] + mod - (k > c[j] ? pre[k - c[j] - 1][j - 1] : 0)) * ifac[k - i] % mod);
        }
        for (int k = i; k <= n; k++) memset(pre[k], 0, sizeof(pre[k]));
    }

    ll ans = 0; for (int i = 0; i <= m; i++) chkadd(ans, f[n][i]);
    cout << ans * fac % mod;
    return 0;
}