#include<bits/stdc++.h>
using namespace std;
// #define LOCAL
#ifdef LOCAL
    #define eprintf(...) fprintf(stderr, __VA_ARGS__)
#else
    #define eprintf(...) 42
#endif // LOCAL
int const nax = 3e5 + 10, mod = 1e9 + 7;

void plusle(int &a, int b) {
    if ((a += b) >= mod) a -= mod;
}
int add (int a, int b) {
    return ((a += b) >= mod) ? a - mod : a;
}
int mul (int a, int b) {
    return 1LL * a * b % mod;
}

int n, k, a[nax];
int f[22][1050];
int c[1020][1020];


int main(){
    scanf("%d %d", &n, &k);
    c[0][0] = 1;
    for (int i = 1 ; i <= 1000 ; ++ i ) {
        c[i][0] = 1 ;
        for (int j = 1 ;j  <= 1000 ; ++ j)
            c[i][j] = add(c[i - 1][j - 1], c[i - 1][j]);
    }

    for(int i = 1 ;i <= k ;i ++)
        scanf("%d", a  + i);

    for (int i = 0 ; i <= a[1] ; ++ i)
        f[1][i] = mul(c[n][i], c[n - i][a[1] - i]);

    for (int j = 2 ; j <= k ; ++ j)
        for (int i = 0 ; i <= n ; ++ i)
            for (int from = 0 ; from <= n - i && i <= a[j]; ++ from)
                plusle(f[j][from + i] ,mul(f[j - 1][from], mul(c[n - from][ i], c[n - i][a[j] - i])));

    printf("%d\n", f[k][n]);
}
/*
    Good Luck
        -Lucina
*/
