import sys
input = sys.stdin.readline

MOD = 10**9+7
N,K=map(int, input().split())
A=list(map(int, input().split()))

f=[1]
for i in range(1,N+1):
    f.append(f[-1]*(K+i)*pow(i,MOD-2,MOD)%MOD)

res=0
for i in range(N):
    res+=A[i]*f[i]%MOD*f[N-1-i]%MOD
    res%=MOD
print(res)