n,k = map(int,input().split())
a = tuple(map(int,input().split()))
mod = 10**9+7
rng = 1001
fctr = [1]
finv = [1]
for i in range(1,rng):
  fctr.append(fctr[-1]*i%mod)
  finv.append(pow(fctr[i],mod-2,mod))
dp = [[0 for i in range(n+1)] for j in range(k+1)]
dp[0][0] = 1
for i in range(1,k+1):
  x = a[i-1]
  for j in range(n+1):
    if dp[i-1][j] == 0:
      continue
    y = dp[i-1][j]*fctr[n-j]*finv[n-x]%mod
    for t in range(min(n-j,x)+1):
      dp[i][j+t]=(dp[i][j+t]+y*fctr[n-t]*finv[n-j-t]*finv[t]*finv[x-t])%mod
print(dp[k][n])