#include <bits/stdc++.h>
using namespace std;
void debug_out() { cerr << endl; }
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
  cerr << " " << to_string(H);
  debug_out(T...);
}
template <class T>
inline bool chmax(T& a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T>
inline bool chmin(T& a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
using ll = long long;
using P = pair<ll, ll>;
constexpr long double PI = 3.14159265358979323846264338327950288L;
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
constexpr ll mod17 = 1e9 + 7;
constexpr ll mod19 = 1e9 + 9;
constexpr ll mod9 = 998244353;
ll mod = mod17;
unordered_map<ll, ll> minvmap;
ll minv(ll a, ll m) {
  auto k = a;
  auto p = minvmap[a];
  if (p != 0) return p;
  ll b = m, u = 1, v = 0;
  while (b) {
    ll t = a / b;
    swap(a -= t * b, b);
    swap(u -= t * v, v);
  }
  p = (u % m + m) % m;
  minvmap[k] = p;
  return p;
}
struct mint {
  ll x;
  mint() : x(0) {}
  mint(ll x) : x((x % mod + mod) % mod) {}
  mint& fix() {
    x = (x % mod + mod) % mod;
    return *this;
  }
  mint operator-() const { return mint(0) - *this; }
  mint& operator+=(const mint& a) {
    if ((x += a.x) >= mod) x -= mod;
    return *this;
  }
  mint& operator-=(const mint& a) {
    if ((x += mod - a.x) >= mod) x -= mod;
    return *this;
  }
  mint& operator*=(const mint& a) {
    (x *= a.x) %= mod;
    return *this;
  }
  mint& operator/=(const mint& a) {
    (x *= minv(a.x, mod)) %= mod;
    return *this;
  }
  mint operator+(const mint& a) const { return mint(*this) += a; }
  mint operator-(const mint& a) const { return mint(*this) -= a; }
  mint operator*(const mint& a) const { return mint(*this) *= a; }
  mint operator/(const mint& a) const { return mint(*this) /= a; }
  bool operator<(const mint& a) const { return x < a.x; }
  bool operator==(const mint& a) const { return x == a.x; }
};
template <typename T>
T mod_pow(T a, ll x) {
  T res = 1;
  while (x > 0) {
    if (x & 1) res *= a;
    a *= a;
    x >>= 1;
  }
  return res;
}
class combination {
 public:
  std::vector<mint> fact;

 public:
  std::vector<mint> inv;
  combination(int n) {
    fact.resize(n + 1);
    inv.resize(n + 1);
    fact[0] = 1;
    for (int i = 1; i <= n; i++) {
      fact[i] = fact[i - 1] * i;
    }
    inv[n] = mint(1) / fact[n];
    for (int i = n - 1; i >= 0; i--) {
      inv[i] = inv[i + 1] * (i + 1);
    }
  }

 public:
  mint get(int n, int r) {
    if (n < r || n < 0 || r < 0) return 0;
    return fact[n] * inv[r] * inv[n - r];
  }

 public:
  mint p(int n, int r) {
    if (n < r || n < 0) return 0;
    return fact[n] * inv[n - r];
  }
};
class CCookieDistribution {
 public:
  void solve(istream& cin, ostream& cout) {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    int n, k;
    cin >> n >> k;
    vector<int> a(k);
    for (int i = 0; i < (int)(n); i++) {
      cin >> a[i];
    }
    auto comb = combination(n + 1);
    vector<vector<mint>> dp(k + 1, vector<mint>(n + 1));
    dp[0][0] = comb.fact[n];
    for (int i = 0; i < (int)(k); i++) {
      for (int x = 0; x < (int)(a[i] + 1); x++) {
        mint r = comb.get(n - x, a[i] - x) * comb.inv[x];
        for (int j = 0; j <= n; j++) {
          if (j + x > n) break;
          dp[i + 1][j + x] += dp[i][j] * r;
        }
      }
    }
    cout << dp[k][n].x << endl;
  }
};
signed main() {
  CCookieDistribution solver;
  std::istream& in(std::cin);
  std::ostream& out(std::cout);
  solver.solve(in, out);
  return 0;
}
