#include <bits/stdc++.h>

using namespace std;

struct fast_ios {
    fast_ios() {
        cin.tie(nullptr);
        ios::sync_with_stdio(false);
        cout << fixed << setprecision(10);
    };
} fast_ios_;

template<typename A, typename B>
bool chkmin(A &a, const B &b) {
    if (b < a) {
        a = b;
        return true;
    }
    return false;
}

template<typename A, typename B>
bool chkmax(A &a, const B &b) {
    if (b > a) {
        a = b;
        return true;
    }
    return false;
}

template<typename T>
istream &operator>>(istream &stream, vector<T> &vec) {
    for (auto &x : vec) stream >> x;
    return stream;
}

void scan() {}

template<class T, class ...Args>
void scan(T &a, Args &...rest) {
    cin >> a;
    scan(rest...);
}

using ll = long long;
using vl = vector<ll>;
using vb = vector<bool>;
using vi = vector<int>;
template<typename T> using vv = vector<vector<T>>;
#define rng(i, a, b) for(int i = (int)(a); i < (int)(b); ++i)
#define up(i, a, b) for (int i = int(a); i <= int(b); ++i)
#define down(i, b, a) for (int i = int(b); i >= int(a); i--)
#define rep(n) for(int _iter_##n = 0, _num_##n = (int)n; _iter_##n < _num_##n; ++_iter_##n)
#define FOR(x, cont) for (const auto &x: cont)
#define For(x, cont) for (auto &x: cont)
#define all(x) begin(x), end(x)
#define pb push_back
#define mp make_pair
#define eb emplace_back
#define ep emplace
#define SZ(x) (int)(x).size()
#define UNIQ(vec) (vec).erase(unique(all(vec)), end(vec))
#define LB(cont, x) int(lower_bound(all(cont), x) - begin(cont))
#define UB(cont, x) int(upper_bound(all(cont), x) - begin(cont))

template<typename T>
ostream &operator<<(ostream &stream, const vector<T> &vec) {
    if (!vec.empty()) {
        stream << vec[0];
        for (size_t i = 1; i != vec.size(); ++i)
            stream << ' ' << vec[i];
    }
    return stream;
}

template<typename T>
void print(const vector<T> &t) { cout << t << '\n'; }

template<typename T>
void print(const vector<vector<T>> &t) {
    for (const auto &row : t) {
        print(row);
    }
}

template<typename T>
void print(const T &t) { cout << t << ' '; }

template<typename T, typename ...Args>
void print(const T &t, const Args &...rest) {
    print(t);
    print(rest...);
}

template<typename T>
void println(const T &t) { cout << t << '\n'; }

template<typename T, typename ...Args>
void println(const T &t, const Args &...rest) {
    print(t);
    println(rest...);
}


// debug code by tourist
string to_string(const string &s) {
    return '"' + s + '"';
}

string to_string(const char *s) {
    return to_string((string) s);
}

string to_string(bool b) {
    return (b ? "true" : "false");
}

template<typename A, typename B>
string to_string(pair<A, B> p) {
    return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}

template<typename A>
string to_string(A v) {
    bool first = true;
    string res = "{";
    for (const auto &x : v) {
        if (!first) {
            res += ", ";
        }
        first = false;
        res += to_string(x);
    }
    res += "}";
    return res;
}

void debug_out() { cerr << endl; }

template<typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
    cerr << " " << to_string(H);
    debug_out(T...);
}

#ifdef LOCAL
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define debug(...) 42
#endif

// tourist's modular-arithmetic class
template<typename T>
T inverse(T a, T m) {
    T u = 0, v = 1;
    while (a != 0) {
        T t = m / a;
        m -= t * a;
        swap(a, m);
        u -= t * v;
        swap(u, v);
    }
    assert(m == 1);
    return u;
}

template<typename T>
class Modular {
public:
    using Type = typename decay<decltype(T::value)>::type;

    constexpr Modular() : value() {}

    template<typename U>
    Modular(const U &x) {
        value = normalize(x);
    }

    template<typename U>
    static Type normalize(const U &x) {
        Type v;
        if (-mod() <= x && x < mod()) v = static_cast<Type>(x);
        else v = static_cast<Type>(x % mod());
        if (v < 0) v += mod();
        return v;
    }

    const Type &operator()() const { return value; }

    template<typename U>
    explicit operator U() const { return static_cast<U>(value); }

    constexpr static Type mod() { return T::value; }

    Modular &operator+=(const Modular &other) {
        if ((value += other.value) >= mod()) value -= mod();
        return *this;
    }

    Modular &operator-=(const Modular &other) {
        if ((value -= other.value) < 0) value += mod();
        return *this;
    }

    template<typename U>
    Modular &operator+=(const U &other) { return *this += Modular(other); }

    template<typename U>
    Modular &operator-=(const U &other) { return *this -= Modular(other); }

    Modular &operator++() { return *this += 1; }

    Modular &operator--() { return *this -= 1; }

    Modular operator++(int) {
        Modular result(*this);
        *this += 1;
        return result;
    }

    Modular operator--(int) {
        Modular result(*this);
        *this -= 1;
        return result;
    }

    Modular operator-() const { return Modular(-value); }

    template<typename U = T>
    enable_if_t<is_same<typename Modular<U>::Type, int>::value, Modular> &operator*=(const Modular &rhs) {
#ifdef _WIN32
        uint64_t x = static_cast<int64_t>(value) * static_cast<int64_t>(rhs.value);
        uint32_t xh = static_cast<uint32_t>(x >> 32), xl = static_cast<uint32_t>(x), d, m;
        asm(
        "divl %4; \n\t"
        : "=a" (d), "=d" (m)
        : "d" (xh), "a" (xl), "r" (mod())
        );
        value = m;
#else
        value = normalize(static_cast<int64_t>(value) * static_cast<int64_t>(rhs.value));
#endif
        return *this;
    }

    template<typename U = T>
    enable_if_t<is_same<typename Modular<U>::Type, int64_t>::value, Modular> &operator*=(const Modular &rhs) {
        int64_t q = static_cast<int64_t>(static_cast<long double>(value) * rhs.value / mod());
        value = normalize(value * rhs.value - q * mod());
        return *this;
    }

    template<typename U = T>
    enable_if_t<!is_integral<typename Modular<U>::Type>::value, Modular> &operator*=(const Modular &rhs) {
        value = normalize(value * rhs.value);
        return *this;
    }

    Modular &operator/=(const Modular &other) { return *this *= Modular(inverse(other.value, mod())); }

    template<typename U>
    friend const Modular<U> &abs(const Modular<U> &v) { return v; }

    template<typename U>
    friend bool operator==(const Modular<U> &lhs, const Modular<U> &rhs);

    template<typename U>
    friend bool operator<(const Modular<U> &lhs, const Modular<U> &rhs);

    template<typename U>
    friend std::istream &operator>>(std::istream &stream, Modular<U> &number);

private:
    Type value;
};

template<typename T>
bool operator==(const Modular<T> &lhs, const Modular<T> &rhs) { return lhs.value == rhs.value; }

template<typename T, typename U>
bool operator==(const Modular<T> &lhs, U rhs) { return lhs == Modular<T>(rhs); }

template<typename T, typename U>
bool operator==(U lhs, const Modular<T> &rhs) { return Modular<T>(lhs) == rhs; }

template<typename T>
bool operator!=(const Modular<T> &lhs, const Modular<T> &rhs) { return !(lhs == rhs); }

template<typename T, typename U>
bool operator!=(const Modular<T> &lhs, U rhs) { return !(lhs == rhs); }

template<typename T, typename U>
bool operator!=(U lhs, const Modular<T> &rhs) { return !(lhs == rhs); }

template<typename T>
bool operator<(const Modular<T> &lhs, const Modular<T> &rhs) { return lhs.value < rhs.value; }

template<typename T>
Modular<T> operator+(const Modular<T> &lhs, const Modular<T> &rhs) { return Modular<T>(lhs) += rhs; }

template<typename T, typename U>
Modular<T> operator+(const Modular<T> &lhs, U rhs) { return Modular<T>(lhs) += rhs; }

template<typename T, typename U>
Modular<T> operator+(U lhs, const Modular<T> &rhs) { return Modular<T>(lhs) += rhs; }

template<typename T>
Modular<T> operator-(const Modular<T> &lhs, const Modular<T> &rhs) { return Modular<T>(lhs) -= rhs; }

template<typename T, typename U>
Modular<T> operator-(const Modular<T> &lhs, U rhs) { return Modular<T>(lhs) -= rhs; }

template<typename T, typename U>
Modular<T> operator-(U lhs, const Modular<T> &rhs) { return Modular<T>(lhs) -= rhs; }

template<typename T>
Modular<T> operator*(const Modular<T> &lhs, const Modular<T> &rhs) { return Modular<T>(lhs) *= rhs; }

template<typename T, typename U>
Modular<T> operator*(const Modular<T> &lhs, U rhs) { return Modular<T>(lhs) *= rhs; }

template<typename T, typename U>
Modular<T> operator*(U lhs, const Modular<T> &rhs) { return Modular<T>(lhs) *= rhs; }

template<typename T>
Modular<T> operator/(const Modular<T> &lhs, const Modular<T> &rhs) { return Modular<T>(lhs) /= rhs; }

template<typename T, typename U>
Modular<T> operator/(const Modular<T> &lhs, U rhs) { return Modular<T>(lhs) /= rhs; }

template<typename T, typename U>
Modular<T> operator/(U lhs, const Modular<T> &rhs) { return Modular<T>(lhs) /= rhs; }

template<typename T, typename U>
Modular<T> power(const Modular<T> &a, const U &b) {
    assert(b >= 0);
    Modular<T> x = a, res = 1;
    U p = b;
    while (p > 0) {
        if (p & 1) res *= x;
        x *= x;
        p >>= 1;
    }
    return res;
}

template<typename T>
bool IsZero(const Modular<T> &number) {
    return number() == 0;
}

template<typename T>
string to_string(const Modular<T> &number) {
    return to_string(number());
}

template<typename T>
std::ostream &operator<<(std::ostream &stream, const Modular<T> &number) {
    return stream << number();
}

template<typename T>
std::istream &operator>>(std::istream &stream, Modular<T> &number) {
    typename common_type<typename Modular<T>::Type, int64_t>::type x;
    stream >> x;
    number.value = Modular<T>::normalize(x);
    return stream;
}

constexpr int md = 1000000007;
using Mint = Modular<std::integral_constant<decay<decltype(md)>::type, md>>;

template<typename T>
struct Binom {
    vector<T> fact_, inv_fact_;

    explicit Binom(int n) : fact_(n + 1), inv_fact_(n + 1) {
        fact_[0] = 1;
        up (i, 1, n) fact_[i] = fact_[i - 1] * i;
        inv_fact_[n] = 1 / fact_[n];
        down (i, n, 1) {
            inv_fact_[i - 1] = inv_fact_[i] * i;
        }
    }

    T binom(int x, int y) const {
        assert(x <= SZ(fact_) - 1);
        assert(x >= 0 && y >= 0);
        if (x < y) return 0;
        return fact_[x] * inv_fact_[y] * inv_fact_[x - y];
    }

    T fact(int n) const {
        assert(n < SZ(fact_));
        return fact_[n];
    }

    T inv_fact(int n) const {
        assert(n < SZ(inv_fact_));
        return inv_fact_[n];
    }
};

int main() {
#if defined LOCAL
    ifstream in("in.txt");
    cin.rdbuf(in.rdbuf());
#endif
    int n, k;
    scan(n, k);
    vi a(k);
    scan(a);
    vv<Mint> f(k, vector<Mint>(n + 1));
    Binom<Mint> b(n);
    for (int i = 0; i <= a[0]; ++i) {
        f[0][i] = b.binom(n - i, a[0] - i) * b.inv_fact(i);
    }
    rng (i, 0, k - 1) {
        up (j, 0, n) {
            if (f[i][j] != 0) {
                up (c, 0, min(a[i + 1], n - j)) {
                    f[i + 1][j + c] += f[i][j] * b.binom(n - c, a[i + 1] - c) * b.inv_fact(c);
                }
            }
        }
    }
    println(f[k - 1][n] * b.fact(n));
    return 0;
}

Measured memory_bytes: 384