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

dic = {}
base = 1
for i in range(n+1):
    dic[(i+k,i)] = base
    base *= i+1+k
    base *= pow(i+1,mod-2,mod)
    base %= mod
    
ans = 0
for i,a in enumerate(A):
    count = dic[(i+k,i)]*dic[(n-1-i+k,n-1-i)]*a%mod
    ans += count
    ans %= mod
print(ans)