// need
#include <iostream>
#include <algorithm>
// data structure
#include <bitset>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>
#include <complex>
//#include <deque>
#include <valarray>
#include <unordered_map>
#include <unordered_set>
#include <array>
// etc
#include <cassert>
#include <cmath>
#include <functional>
#include <iomanip>
#include <chrono>
#include <random>
#include <numeric>

// input
#define INIT std::ios::sync_with_stdio(false);std::cin.tie(0);
#define VAR(type, ...)type __VA_ARGS__;MACRO_VAR_Scan(__VA_ARGS__);
template<typename T> void MACRO_VAR_Scan(T& t) { std::cin >> t; }
template<typename First, typename...Rest>void MACRO_VAR_Scan(First& first, Rest& ...rest) { std::cin >> first; MACRO_VAR_Scan(rest...); }
#define VEC_ROW(type, n, ...)std::vector<type> __VA_ARGS__;MACRO_VEC_ROW_Init(n, __VA_ARGS__); for(int w_=0; w_<n; ++w_){MACRO_VEC_ROW_Scan(w_, __VA_ARGS__);}
template<typename T> void MACRO_VEC_ROW_Init(int n, T& t) { t.resize(n); }
template<typename First, typename...Rest>void MACRO_VEC_ROW_Init(int n, First& first, Rest& ...rest) { first.resize(n); MACRO_VEC_ROW_Init(n, rest...); }
template<typename T> void MACRO_VEC_ROW_Scan(int p, T& t) { std::cin >> t[p]; }
template<typename First, typename...Rest>void MACRO_VEC_ROW_Scan(int p, First& first, Rest& ...rest) { std::cin >> first[p]; MACRO_VEC_ROW_Scan(p, rest...); }
#define VEC(type, c, n) std::vector<type> c(n);for(auto& i:c)std::cin>>i;
#define MAT(type, c, m, n) std::vector<std::vector<type>> c(m, std::vector<type>(n));for(auto& R:c)for(auto& w:R)std::cin>>w;
// output
#define OUT(dist) std::cout<<(dist);
#define FOUT(n, dist) std::cout<<std::fixed<<std::setprecision(n)<<(dist);
#define SOUT(n, c, dist) std::cout<<std::setw(n)<<std::setfill(c)<<(dist);
#define SP std::cout<<" ";
#define TAB std::cout<<"\t";
#define BR std::cout<<"\n";
#define SPBR(w, n) std::cout<<(w + 1 == n ? '\n' : ' ');
#define ENDL std::cout<<std::endl;
#define FLUSH std::cout<<std::flush;
#define SHOW(dist) {std::cerr << #dist << "\t:" << (dist) << "\n";}
#define SHOWVECTOR(v) {std::cerr << #v << "\t:";for(const auto& xxx : v){std::cerr << xxx << " ";}std::cerr << "\n";}
#define SHOWVECTOR2(v) {std::cerr << #v << "\t:\n";for(const auto& xxx : v){for(const auto& yyy : xxx){std::cerr << yyy << " ";}std::cerr << "\n";}}
#define SHOWQUEUE(a) {auto tmp(a);std::cerr << #a << "\t:";while(!tmp.empty()){std::cerr << tmp.front() << " ";tmp.pop();}std::cerr << "\n";}
#define SHOWSTACK(a) {auto tmp(a);std::cerr << #a << "\t:";while(!tmp.empty()){std::cerr << tmp.top() << " ";tmp.pop();}std::cerr << "\n";}
// utility
#define ALL(a) (a).begin(),(a).end()
#define FOR(w, a, n) for(int w=(a);w<(n);++w)
#define RFOR(w, a, n) for(int w=(n)-1;w>=(a);--w)
#define REP(w, n) for(int w=0;w<int(n);++w)
#define RREP(w, n) for(int w=int(n)-1;w>=0;--w)
#define IN(a, x, b) (a<=x && x<b)
template<class T> inline T CHMAX(T& a, const T b) { return a = (a < b) ? b : a; }
template<class T> inline T CHMIN(T& a, const T b) { return a = (a > b) ? b : a; }
// test
template<class T> using V = std::vector<T>;
template<class T> using VV = V<V<T>>;

template<typename S, typename T>
std::ostream& operator<<(std::ostream& os, std::pair<S, T> p) {
	os << "(" << p.first << ", " << p.second << ")"; return os;
}

#define random_shuffle "USE std::shuffle!";

// type/const
#define int ll
using ll = long long;
using ull = unsigned long long;
using ld = long double;
using PAIR = std::pair<int, int>;
using PAIRLL = std::pair<ll, ll>;
constexpr int INFINT = (1 << 30) - 1;                    // 1.07x10^ 9
constexpr int INFINT_LIM = (1LL << 31) - 1;              // 2.15x10^ 9
constexpr ll INFLL = 1LL << 60;                          // 1.15x10^18
constexpr ll INFLL_LIM = (1LL << 62) - 1 + (1LL << 62);  // 9.22x10^18
constexpr double EPS = 1e-10;
constexpr int MOD = 1000000007;
constexpr double PI = 3.141592653589793238462643383279;
template<class T, size_t N> void FILL(T(&a)[N], const T& val) { for (auto& x : a) x = val; }
template<class ARY, size_t N, size_t M, class T> void FILL(ARY(&a)[N][M], const T& val) { for (auto& b : a) FILL(b, val); }
template<class T> void FILL(std::vector<T>& a, const T& val) { for (auto& x : a) x = val; }
template<class ARY, class T> void FILL(std::vector<std::vector<ARY>>& a, const T& val) { for (auto& b : a) FILL(b, val); }
// ------------>8------------------------------------->8------------

class ModInt {
	friend std::istream& operator>>(std::istream& is, ModInt& obj);
public:
	int val;
	ModInt() : val(0) {}
	ModInt(int n) : val(n% MOD) { if (val < 0) val += MOD; }
	ModInt& operator=(const int& r) { val = r % MOD; if (r < 0) val += MOD; return *this; }
	ModInt operator+() const { return *this; }
	ModInt operator-() const { ModInt res; res.val = (val) ? MOD - val : 0; return res; }
	ModInt& operator+=(const ModInt& r) {
		if ((val += r.val) >= MOD) val -= MOD;
		return *this;
	}
	ModInt& operator+=(const int& r) { return *this += ModInt(r); }
	ModInt& operator-=(const ModInt& r) { return *this += -r; }
	ModInt& operator-=(const int& r) { return *this -= ModInt(r); }
	ModInt& operator++() { return *this += 1; }
	ModInt& operator++(signed tmp) { return *this += 1; }
	ModInt& operator--() { return *this += MOD - 1; }
	ModInt& operator--(signed tmp) { return *this += MOD - 1; }
	ModInt& operator*=(const ModInt& r) {
		(val *= r.val) %= MOD;
		return *this;
	}
	ModInt& operator*=(const int& r) { return *this *= ModInt(r); }
	ModInt& operator^=(int p) { // O(log(p))
		ModInt res(1);
		while (p) {
			if (p & 1) res *= *this;
			*this *= *this;
			p >>= 1;
		}
		return *this = res;
	}
	ModInt& operator/=(const ModInt& r) { return *this *= r ^ (MOD - 2); }
	ModInt& operator/=(const int& r) { return *this /= ModInt(r); }
	ModInt operator+(const ModInt& r) const {
		auto res(*this);
		return res += r;
	}
	ModInt operator-(const ModInt& r) const {
		auto res(*this);
		return res -= r;
	}
	ModInt operator*(const ModInt& r) const {
		auto res(*this);
		return res *= r;
	}
	ModInt operator/(const ModInt& r) const {
		auto res(*this);
		return res /= r;
	}
	ModInt operator+(const int& r) const {
		auto res(*this);
		return res += r;
	}
	ModInt operator-(const int& r) const {
		auto res(*this);
		return res -= r;
	}
	ModInt operator*(const int& r) const {
		auto res(*this);
		return res *= r;
	}
	ModInt operator^(const int& r) const {
		auto res(*this);
		return res ^= r;
	}
	ModInt operator/(const int& r) const {
		auto res(*this);
		return res /= r;
	}
};
std::ostream& operator<<(std::ostream& os, const ModInt& obj) {
	os << obj.val;
	return os;
}
/* friend */ std::istream& operator>>(std::istream& is, ModInt& obj) {
	is >> obj.val;
	obj.val %= MOD;
	if (obj.val < 0) obj.val += MOD;
	return is;
}
/** ModInt **/

const signed FACT_MAX_N = 1000006;
ModInt fact[FACT_MAX_N];
ModInt factInv[FACT_MAX_N];
struct INIT_FACT {
	INIT_FACT() {
		fact[0] = 1;
		for (int i = 1; i < FACT_MAX_N; ++i) fact[i] = fact[i - 1] * i;
		factInv[FACT_MAX_N - 1] = 1;
		factInv[FACT_MAX_N - 1] /= fact[FACT_MAX_N - 1];
		for (int i = FACT_MAX_N - 2; i >= 0; --i) factInv[i] = factInv[i + 1] * (i + 1);
	}
} init_fact;

ModInt Permutation(int n, int r) {
	if (r == 0) return 1;
	if (n < r) return 0;
	return fact[n] * factInv[n - r];
}
ModInt Combination(int n, int r) {
	if (r == 0) return 1;
	if (n < r) return 0;
	return fact[n] * factInv[n - r] * factInv[r];
}

ModInt dp[22][1003];

signed main() {
	INIT;

	VAR(int, n, k);
	VEC(int, a, k);

	dp[0][0] = 1;
	REP(i, k) REP(j, n + 1) {
		REP(l, a[i] + 1) {
			if (j + l > n) break; // n-l個からa[i]-l個選ぶ場合の数
			dp[i + 1][j + l] += dp[i][j] * Combination(n - j, l) * Combination(n - l, a[i] - l);
		}
	}
	OUT(dp[k][n])BR;

	return 0;
}

Measured memory_bytes: 16128