#pragma GCC optimize(3, "Ofast", "inline")
#include <bits/stdc++.h>
using namespace std;
#define int long long
const int maxn = 1e6 + 9;
const int mod = 1e9 + 7;
const int fur = 5010;
int prefam[fur], family[fur];
int famcosts[fur];
int fact[maxn];
void init()
{
    fact[0] = 1;
    for (int i = 1; i <= maxn; i++)
    {
        fact[i] = (fact[i - 1] * i) % mod;
    }
}
signed main()
{
    init();
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int n, h;
    cin >> n >> h;
    for (int i = 1; i <= n; i++)
    {
        cin >> family[i];
        prefam[i] = prefam[i - 1] + family[i];
    }
    if (!h)
    {
        cout << fact[n] << endl;
        return 0;
    }
    for (int i = 1; i <= h; i++)
    {
        int now = fact[prefam[i]] % mod;
        for (int j = 1; j < i; j++)
        {
            now = (now + mod - (famcosts[j] * fact[prefam[i] - prefam[j]] % mod)) % mod;
        }
        famcosts[i] = now;
    }
    int ans = fact[n];
    for (int i = 1; i <= h; i++)
    {
        ans = (mod + ans - (famcosts[i] * fact[n - prefam[i]] % mod)) % mod;
    }
    cout << ans << endl;
}