n,k = map(int,input().split())
a = list(map(int,input().split()))
mod  = 10**9 + 7

## nCkのmodを求める関数
# テーブルを作る(前処理)
max = 2 * 10**5 + 100
fac, finv, inv = [0]*max, [0]*max, [0]*max

def comInit(max):
    fac[0] = fac[1] = 1
    finv[0] = finv[1] = 1
    inv[1] = 1

    for i in range(2,max):
      fac[i] = fac[i-1]* i% mod
      inv[i] = mod - inv[mod%i] * (mod // i) % mod
      finv[i] = finv[i-1] * inv[i] % mod

comInit(max)


left = [1] * (n+1)
# right = [1] * (n+2)

for i in range(2,n+1):
    left[i] = (left[i-1] * (k+i-1) * inv[i-1])%mod
    # right[n+1-i] = (right[n+2-i] * (k+i-1) * inv[i])%mod

ans = 0
for i,ai in enumerate(a,1):
    tmp = (ai * left[i] * left[-1*i])%mod
    ans += tmp
    ans %= mod

print(ans)