N, K = map(int, input().split())
A = list(map(int, input().split()))

def combs_mod(n,k,mod):
  #nC0からnCkまで
  inv = [1]*(n+1)
  for i in range(1,n):
    inv[i] = pow(i,mod-2,mod)
  ans = [1]*(n+1)
  for i in range(1,n):
    ans[i] = ans[i-1]*(k+i)*inv[i]%mod
  return ans

ans = 0
mod = 10**9+7
combs = combs_mod(N,K,mod)
for i in range(N):
  ans += A[i]*combs[i]*combs[N-1-i]
  ans %= mod
print(ans)