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

#define mod 1000000007
#define MAX_N 200010
long long inv[MAX_N];
long long factorial[MAX_N];
long long inv_factorial[MAX_N];

void GetInv(){
    for (int i = 1; i < MAX_N; i++) {
        if (i == 1) inv[i] = 1;
        else {
            inv[i] = (mod - (mod / i) * inv[mod % i]) % mod;
            if (inv[i] < 0) inv[i] += mod;
        }
    }
}
void GetFactorial(){
    factorial[0] = 1; inv_factorial[0] = 1;
    for (int i = 1; i < MAX_N; i++) {
        factorial[i] = factorial[i-1] * i;
        factorial[i] %= mod;
        inv_factorial[i] = inv_factorial[i-1] * inv[i];
        inv_factorial[i] %= mod;
    }
}

long long combination(int n, int r) {
    if (n < 0 || r < 0 || n < r) return 0; 
    long long ret = factorial[n] * inv_factorial[r];
    ret %= mod;
    ret *= inv_factorial[n-r];
    return ret % mod;
}

long long modpow(int n, int r) {
    long long ret = 1; long long tmp = (long long) n;
    while (r != 0) {
        if (r % 2) ret *= tmp;
        tmp *= tmp; tmp %= mod; ret %= mod;
        r /= 2;
    }
    return ret;
}

long long dp[21][1010];

int main() {
    GetInv(); GetFactorial();
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    int n, k; cin >> n >> k;
    vector<int> a(k);
    for (int i = 0; i < k; i++) cin >> a[i];
    dp[0][n] = 1;
    for (int i = 0; i < k; i++) {
        for (int j = 0; j <= n; j++) {
            for (int k = 0; k <= j; k++) {
                dp[i+1][j-k] += dp[i][j] * combination(n-k, a[i]-k) % mod * inv_factorial[k] % mod;
                dp[i+1][j-k] %= mod;
            }
        }
    }
    cout << dp[k][0] * factorial[n] % mod << "\n";
    return 0;
}