MX_N=int(1e9)
MX_K=int(1e8)
MX_A=int(1e9)
MOD=int(1e9)+7
def main():
    N,K=map(int,input().split())
    A=list(map(int,input().split()))
    assert(1<=N<=MX_N)
    assert(0<=K<=MX_K)
    for i in range(N):
        assert(1<=A[i]<=MX_A)
    ans=0
    comb=[1 for i in range(N)]
    for i in range(1,N):
        comb[i]=((comb[i-1]*(K+i))%MOD*pow(i,MOD-2,MOD))%MOD
    for i in range(N):
        ans+=(comb[i]*comb[N-1-i])%MOD*A[i]
        ans%=MOD
    return ans

if __name__ == '__main__':
    print(main())