#include<iostream>
using namespace std;
const long mod=1e9+7;
long power(long a,long b){return b?power(a*a%mod,b/2)*(b%2?a:1)%mod:1;}
int N,K;
long A[2<<17];
long S[2<<17];
//H(a,K)=C(a+K-1,K)=C(a+K-1,a-1)
long H[2<<17];
main()
{
	cin>>N>>K;
	for(int i=0;i<N;i++)
	{
		cin>>A[i];
		S[i+1]=S[i]+A[i];
		S[i+1]%=mod;
	}
	if(K==0)
	{
		cout<<S[N]<<endl;
		return 0;
	}
	K--;
	H[1]=1;
	for(int i=2;i<=N;i++)
	{
		H[i]=H[i-1]*(K+i-1)%mod*power(i-1,mod-2)%mod;
	}
	long ans=0,cum=0;
	for(int i=1;i<=N;i++)
	{
		(cum+=H[i])%=mod;
		(ans+=S[i]*cum%mod*H[N-i+1]%mod)%=mod;
	}
	cum=0;
	for(int i=N;i>=1;i--)
	{
		(cum+=H[N-i+1])%=mod;
		(ans+=(mod-S[i-1])*cum%mod*H[i]%mod)%=mod;
	}
	cout<<ans<<endl;
}