import java.io.BufferedReader import java.io.InputStream import java.io.InputStreamReader import java.util.* import kotlin.math.abs import kotlin.math.max import kotlin.math.min val MOD = 1_000_000_007 class Comb(n: Int, val mod: Int) { val F = LongArray(n + 1) val I = LongArray(n + 1) init { F[0] = 1 for (i in 1..n) { F[i] = F[i - 1] * i % mod } I[n] = powMod(F[n], (mod - 2).toLong(), mod) for (i in n - 1 downTo 0) { I[i] = I[i + 1] * (i + 1) % mod } } private fun powMod(a: Long, n: Long, mod: Int): Long { if (n == 0L) return 1 val res = powMod(a * a % mod, n / 2, mod) return if (n % 2 == 1L) res * a % mod else res } fun comb(n: Int, k: Int): Long { return F[n] * I[k] % mod * I[n - k] % mod } fun perm(n: Int, k: Int): Long { return F[n] * I[n - k] % mod } fun inv(x: Int): Long { return I[x] * F[x - 1] % mod } /** * nのグループからk回重複ありで選ぶ組み合わせ数 * n - 1のしきりとkの○で考える */ fun H(n: Int, k: Int) = comb(n + k - 1, k) } class Solver(stream: InputStream, private val out: java.io.PrintWriter) { fun solve() { val N = ni() val K = ni() val A = na(N) var ans = 0L val dp = LongArray(N + 1) dp[0] = 1 val comb = Comb(N, MOD) for (i in 1 .. N) { dp[i] = dp[i - 1] * (K + i) % MOD * comb.inv(i) % MOD } debug(dp) fun c(i: Int): Long { return dp[i - 1] // return comb.comb(i + K - 1, K) } for (i in 0 until N) { ans += c(N - i) * c(i + 1) % MOD * A[i] % MOD } out.println(ans % MOD) } private val isDebug = try { // なんか本番でエラーでる System.getenv("MY_DEBUG") != null } catch (t: Throwable) { false } private var tokenizer: StringTokenizer? = null private val reader = BufferedReader(InputStreamReader(stream), 32768) private fun next(): String { while (tokenizer == null || !tokenizer!!.hasMoreTokens()) { tokenizer = StringTokenizer(reader.readLine()) } return tokenizer!!.nextToken() } private fun ni() = next().toInt() private fun nl() = next().toLong() private fun ns() = next() private fun na(n: Int, offset: Int = 0): IntArray { return map(n) { ni() + offset } } private fun nal(n: Int, offset: Int = 0): LongArray { val res = LongArray(n) for (i in 0 until n) { res[i] = nl() + offset } return res } private fun na2(n: Int, offset: Int = 0): Array { val a = Array(2){IntArray(n)} for (i in 0 until n) { for (e in a) { e[i] = ni() + offset } } return a } private inline fun map(n: Int, f: (Int) -> Int): IntArray { val res = IntArray(n) for (i in 0 until n) { res[i] = f(i) } return res } private inline fun debug(msg: () -> String) { if (isDebug) System.err.println(msg()) } private fun debug(a: LongArray) { debug { a.joinToString(" ") } } private fun debug(a: IntArray) { debug { a.joinToString(" ") } } private fun debug(a: BooleanArray) { debug { a.map { if (it) 1 else 0 }.joinToString("") } } private fun debugDim(A: Array) { if (isDebug) { for (a in A) { debug(a) } } } private fun debugDim(A: Array) { if (isDebug) { for (a in A) { debug(a) } } } /** * 勝手にimport消されるのを防ぎたい */ private fun hoge() { min(1, 2) max(1, 2) abs(-10) } } fun main() { val out = java.io.PrintWriter(System.out) Solver(System.`in`, out).solve() out.flush() }