def inv(a):
    m=10**9+7
    b=m
    (x, lastx) = (0, 1)
    (y, lasty) = (1, 0)
    while b != 0:
        q = a // b
        (a, b) = (b, a % b)
        (x, lastx) = (lastx - q * x, x)
        (y, lasty) = (lasty - q * y, y)
    return lastx % m


def main():
    MOD=10**9+7
    n,k=map(int,input().split())
    a=list(map(int,input().split()))

    frac=[1]
    for i in range(1,n+1):
        frac.append(frac[-1]*i%MOD)
    
    fracinv=[inv(frac[i]) for i in range(n+1)]


    dp=[[0]*(n+1) for _ in range(k)]

    for x in range(a[0]+1):
        dp[0][x]=frac[n]*frac[n-x]*inv(frac[a[0]-x]*frac[n-a[0]]*frac[x])%MOD

    for i in range(k-1):
        ai=a[i+1]
        for j in range(n+1):
            for x in range(ai+1):
                p=j+x
                if p>n: break
                tmp=dp[i][j]
                tmp=tmp*frac[n-x]%MOD
                tmp=tmp*fracinv[ai-x]%MOD
                tmp=tmp*fracinv[n-ai]%MOD
                tmp=tmp*fracinv[x]%MOD
                dp[i+1][p]=(dp[i+1][p]+tmp)%MOD
    print(dp[k-1][n]%MOD)

if __name__ == "__main__":
    main()