from collections import *
from itertools import *
from functools import *
from heapq import *
import sys,math
input = sys.stdin.readline

N,K = map(int,input().split())
A = list(map(int,input().split()))
mod = 10**9 + 7

C = defaultdict(int)
C[K] = 1
for i in range(N):
    C[i+1+K] = C[i+K]*(i+1+K)*pow(i+1,mod-2,mod)%mod


ans = 0
for i,a in enumerate(A):
    
    ans += C[i+K]*C[N-i+K-1]*a
    ans %= mod
print(ans)