#include <iostream>
using namespace std;

const int MAX = 5100;
const long MOD = 1000000007;

long long fac[MAX], finv[MAX], inv[MAX];

// テーブルを作る前処理
void COMinit() {
    fac[0] = fac[1] = 1;
    finv[0] = finv[1] = 1;
    inv[1] = 1;
    for (int i = 2; i < MAX; i++){
        fac[i] = fac[i - 1] * i % MOD;
        inv[i] = MOD - inv[MOD%i] * (MOD / i) % MOD;
        finv[i] = finv[i - 1] * inv[i] % MOD;
    }
}

// 二項係数計算
long long COM(int n, int k){
    if (n < k) return 0;
    if (n < 0 || k < 0) return 0;
    return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD;
}

int main() {
  int N,K;
  cin>>N>>K;
  vector<int>a(N);
  for(int i=0;i<N;i++)cin>>a[i];
  long ans=0;
  for(int i=0;i<N;i++){
    COMinit();
    ans=(ans+C0M(N,a[i]))%MOD;
  }
  cout<<ans<<endl;
}