import sys

sys.setrecursionlimit(10**7)
def I(): return int(sys.stdin.readline().rstrip())
def MI(): return map(int,sys.stdin.readline().rstrip().split())
def LI(): return list(map(int,sys.stdin.readline().rstrip().split()))
def LI2(): return list(map(int,sys.stdin.readline().rstrip()))
def S(): return sys.stdin.readline().rstrip()
def LS(): return list(sys.stdin.readline().rstrip().split())
def LS2(): return list(sys.stdin.readline().rstrip())


N,K = MI()
A = LI()
mod = 10**9+7

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

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

print(ans)