#include<iostream>

#include<cstdio>

#include<cstdlib>

#include<algorithm>

#include<string>

#include<cstring>

#include<cmath>

#include<queue>

using namespace std;

typedef long long ll;

inline int read()

{

    int ans=;

    char last=' ',ch=getchar();

    while(ch<''||ch>'') last=ch,ch=getchar();

    while(ch>=''&&ch<='') ans=ans*+ch-'',ch=getchar();

    if(last=='-') ans=-ans;

    return ans;

}

const int mod=;

ll f[][];

int n,m,x;

ll ans=;

int main()

{

    n=read();m=read();

    f[][]=;

    for(int i=;i<=n;i++){

        f[i][]=;

        for(int j=;j<=;j++)

           f[i][j]=(f[i-][j-]+f[i-][j])%mod;  //防爆炸

    }

    for(int i=;i<=m;i++)

       x=read(),

       ans=ans*f[n][x]%mod,

       n-=x;

    printf("%lld\n",ans);

    return ;

}