class Modulo_Error(Exception):
    pass

class Modulo():
    def __init__(self,a,n):
        self.a=a%n
        self.n=n

    def __str__(self):
        return "{} (mod {})".format(self.a,self.n)

    def __repr__(self):
        return self.__str__()

    #+,-
    def __pos__(self):
        return self

    def __neg__(self):
        return  Modulo(-self.a,self.n)

    #等号,不等号
    def __eq__(self,other):
        if isinstance(other,Modulo):
            return (self.a==other.a) and (self.n==other.n)
        elif isinstance(other,int):
            return (self-other).a==0

    def __neq__(self,other):
        return not(self==other)

    def __le__(self,other):
        a,p=self.a,self.n
        b,q=other.a,other.n
        return (a-b)%q==0 and p%q==0

    def __ge__(self,other):
        return other<=self

    def __lt__(self,other):
        return (self<=other) and (self!=other)

    def __gt__(self,other):
        return (self>=other) and (self!=other)

    #加法
    def __add__(self,other):
        if isinstance(other,Modulo):
            if self.n!=other.n:
                raise Modulo_Error("異なる法同士の演算です.")
            return Modulo(self.a+other.a,self.n)
        elif isinstance(other,int):
            return Modulo(self.a+other,self.n)

    def __radd__(self,other):
        if isinstance(other,int):
            return Modulo(self.a+other,self.n)

    #減法
    def __sub__(self,other):
        return self+(-other)

    def __rsub__(self,other):
        if isinstance(other,int):
            return -self+other

    #乗法
    def __mul__(self,other):
        if isinstance(other,Modulo):
            if self.n!=other.n:
                raise Modulo_Error("異なる法同士の演算です.")
            return Modulo(self.a*other.a,self.n)
        elif isinstance(other,int):
            return Modulo(self.a*other,self.n)

    def __rmul__(self,other):
        if isinstance(other,int):
            return Modulo(self.a*other,self.n)

    #Modulo逆数
    def inverse(self):
        return self.Modulo_Inverse()

    def Modulo_Inverse(self):
        x0, y0, x1, y1 = 1, 0, 0, 1
        a,b=self.a,self.n
        while b != 0:
            q, a, b = a // b, b, a % b
            x0, x1 = x1, x0 - q * x1
            y0, y1 = y1, y0 - q * y1

        if a!=1:
            raise Modulo_Error("{}の逆数が存在しません".format(self))
        else:
            return Modulo(x0,self.n)

    #除法
    def __truediv__(self,other):
        return self*(other.Modulo_Inverse())

    def __rtruediv__(self,other):
        return other*(self.Modulo_Inverse())

    #累乗
    def __pow__(self,other):
        if isinstance(other,int):
            u=abs(other)

            r=Modulo(pow(self.a,u,self.n),self.n)
            if other>=0:
                return r
            else:
                return r.Modulo_Inverse()
        else:
            b,n=other.a,other.n
            if pow(self.a,n,self.n)!=1:
                raise Modulo_Error("矛盾なく定義できません.")
            else:
                return self**b

#================================================
N,K=map(int,input().split())
A=["*"]+list(map(int,input().split()))

Mod=10**9+7

L=[0]*(N+1); L[1]=Modulo(1,Mod)
for i in range(2,N+1):
    L[i]=Modulo(i+K-1,Mod)/Modulo(i-1,Mod)*L[i-1]

R=[0]*(N+1); R[N]=Modulo(1,Mod)
for i in range(N-1,0,-1):
    R[i]=Modulo(N-i+K,Mod)/Modulo(N-i,Mod)*R[i+1]

X=Modulo(0,Mod)
for a,l,r in zip(A[1:],L[1:],R[1:]):
    X+=a*l*r

print(X.a)