import sys
input=lambda: sys.stdin.readline().rstrip()
n,k=map(int,input().split())
A=[int(i) for i in input().split()]
mod=10**9+7

H=[0]*(n+1)
H[0]=1
for i in range(n):
  H[i+1]=(H[i]*(k+i+1)*pow(i+1,mod-2,mod))%mod
ans=0
for i,a in enumerate(A):
  ans=(ans+a*(H[i]*H[n-i-1]))%mod
print(ans)