from operator import itemgetter
from itertools import *
from bisect import *
from collections import *
from heapq import *
from fractions import Fraction
import sys

sys.setrecursionlimit(10 ** 6)

def II(): return int(sys.stdin.readline())
def MI(): return map(int, sys.stdin.readline().split())
def LI(): return list(map(int, sys.stdin.readline().split()))
def SI(): return sys.stdin.readline()[:-1]
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
int1 = lambda x: int(x) - 1
def MI1(): return map(int1, sys.stdin.readline().split())
def LI1(): return list(map(int1, sys.stdin.readline().split()))
p2D = lambda x: print(*x, sep="\n")
dij = [(1, 0), (0, 1), (-1, 0), (0, -1)]

md=10**9+7
n,k=MI()
aa=MI()
hh=[-1,1]
for i in range(1,n):hh.append(hh[-1]*(k+i)*pow(i,md-2,md)%md)
ans=0
for i,a in enumerate(aa):
    ans+=a*hh[i+1]*hh[n-i]
    ans%=md
print(ans)