MOD = 10**9+7
N,K = map(int,input().split())
A = [0]+list(map(int,input().split()))
if K==0:
    print(sum(A)%MOD)
else:
    B = [0 for _ in range(N+1)]
    B[0] = 1
    C = [0 for _ in range(N+1)]
    C[0] = 1
    for i in range(1,N+1):
        B[i] = (B[i-1]*(K-1+i))%MOD
        C[i] = (C[i-1]*i)%MOD
    D = [1 for _ in range(N+1)]
    for i in range(1,N+1):
        D[i] = (D[i-1]+B[i]*pow(C[i],MOD-2,MOD))%MOD
    ans = 0
    for m in range(1,N+1):
        ans = (ans+A[m]*D[m-1]*D[N-m])%MOD
    print(ans)