#include <iostream>
#include<vector>
#include<algorithm>
#include<string>
#include<map>
#include<set>
#include<stack>
#include<queue>
#include<math.h>
using namespace std;
typedef long long ll;
#define int long long
#define double long double
typedef vector<int> VI;
typedef pair<int, int> pii;
typedef vector<pii> VP;
typedef vector<string> VS;
typedef priority_queue<int> PQ;
template<class T>bool chmax(T &a, const T &b) { if (a < b) { a = b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b < a) { a = b; return 1; } return 0; }
#define fore(i,a) for(auto &i:a)
#define REP(i,n) for(int i=0;i<n;i++)
#define eREP(i,n) for(int i=0;i<=n;i++)
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define eFOR(i,a,b) for(int i=(a);i<=(b);++i)
#define SORT(c) sort((c).begin(),(c).end())
#define rSORT(c) sort((c).rbegin(),(c).rend())
#define LB(x,a) lower_bound((x).begin(),(x).end(),(a))
#define UB(x,a) upper_bound((x).begin(),(x).end(),(a))
#define INF 1000000000
#define LLINF 9223372036854775807
#define mod 1000000007
#define eps 1e-12 
//priority_queue<int,vector<int>, greater<int> > q2;
int modpow(int a, int p) {
	if (p == 0) return 1;
	if (p % 2 == 0) {

		int halfP = p / 2;
		int half = modpow(a, halfP);

		return half * half % mod;
	}
	else {

		return a * modpow(a, p - 1) % mod;
	}
}
int comb(int a, int b) {
	if (b > a - b) return comb(a, a - b);


	int ansMul = 1;
	int ansDiv = 1;
	for (int i = 0; i < b; i++)
	{
		ansMul *= (a - i);
		ansDiv *= (i + 1);
		ansMul %= mod;
		ansDiv %= mod;
	}

	int ans = ansMul * modpow(ansDiv, mod - 2) % mod;

	return ans;
}
long long modinv(long long a) {
	return modpow(a, mod - 2);
}
signed main() {
	cin.tie(0);
	ios::sync_with_stdio(false);

	int N, K; cin >> N >> K;
	VI A(N);
	REP(i, N)cin >> A[i];
	int ans = 0;
	VI C(K + N + 10);
	C[K] = comb(K, K);
	for (int i = K + 1; i < C.size(); i++) {
		C[i] = C[i - 1] * i;
		C[i] %= mod;
		C[i] *= modinv(i - K);
		C[i] %= mod;
	}

	REP(i, N) {
		int cnt = A[i];

		cnt *= C[i + K];
		cnt %= mod;

		cnt *= C[N - i + K - 1];
		cnt %= mod;

		ans += cnt;
		ans %= mod;
	}



	cout << ans << endl;
	return 0;
}