N,K=map(int,input().split())
A=list(map(int,input().split()))
if K==0:
  print(sum(A)%(10**9+7))
  exit()
X=[K]
mod=10**9+7
for i in range(N+1):
  X.append(X[-1]*pow(i+2,mod-2,mod)*(K+i+1)%mod)
P=0
for i in range(N):
  P=(P+A[i]*(1+i)*(N-i)*X[i]*X[N-i-1])%mod
print(P*pow(pow(K,mod-2,mod),2,mod)%mod)