n,k=map(int,input().split())
a=list(map(int,input().split()))
mod=10**9+7
ans=0
f=[1]
for i in range(1,n):
  f.append(f[-1]*(k+i)*pow(i,mod-2,mod)%mod)
for i in range(n):
  x=(i+1)
  y=(n-i)
  ans+=f[i]*f[n-i-1]*a[i]
  ans%=mod
print(ans)