k = 72
kk = k // 4
K = 1<<k
nu = lambda L: int("".join([hex(K+a)[3:] for a in L[::-1]]), 16)
st = lambda n: hex(n)[2:]
li = lambda s, l, r: [int(a, 16) % P if len(a) else 0 for a in [s[-(i+1)*kk:-i*kk] for i in range(l, r)]]

def grow(d, v, h):
    h += [0] * d
    f = [(-1 if (i+d) % 2 else 1) * fainv[i] * fainv[d-i] % P * h[i] % P for i in range(d+1)]
    nuf = nu(f)
    a = d * inv[v] % P
    t = [1] * (3*d+3)
    for i in range(1, 3*d+3): t[i] = t[i-1] * (a - d + i - 1) % P
    ti = [1] * (3*d+3)
    ti[-1] = pow(t[-1], P-2, P)
    for i in range(1, 3*d+3)[::-1]: ti[i-1] = ti[i] * (a - d + i - 1) % P
    iv = [1] * (3*d+3)
    for i in range(1, 3*d+3):
        iv[i] = ti[i] * t[i-1] % P

    ###
    g = [inv[i] for i in range(1, 2*d+2)]
    fg = li(st(nuf * nu(g)), d, d * 2 + 1)
    for i in range(d):
        h[i+d+1] = fg[i] * fa[d+i+1] % P * fainv[i] % P

    ###
    g = [iv[i] for i in range(1, 2*d+2)]
    fg = li(st(nuf * nu(g)), d, d * 2 + 1)
    for i in range(d+1):
        h[i] = h[i] * (fg[i] * t[d+i+1] % P * ti[i] % P) % P

    ###
    g = [iv[i] for i in range(d+2, 3*d+3)]
    fg = li(st(nuf * nu(g)), d, d * 2 + 1)
    for i in range(d):
        h[i+d+1] = h[i+d+1] * (fg[i] * t[2*d+i+2] % P * ti[d+i+1] % P) % P

    return h

# Create a table of the factorial of the first v+2 multiples of v, i.e., [0!, v!, 2v!, ..., (v(v+1))!]
def create_table(v):
    s = 1
    X = [1, v+1]
    while s < v:
        X = grow(s, v, X)
        s *= 2

    table = [1]
    for x in X:
        table.append(table[-1] * x % P)
    return table

def fact(i, table):
    a = table[i//v]
    for j in range(i//v*v+1, i+1):
        a = a * j % P
    return a

P = 10**9+7

N = 10**8
v = 1 << (N.bit_length() + 1) // 2
fa = [1] * (2*v+2)
fainv = [1] * (2*v+2)
for i in range(2*v+1):
    fa[i+1] = fa[i] * (i+1) % P
fainv[-1] = pow(fa[-1], P-2, P)
for i in range(2*v+1)[::-1]:
    fainv[i] = fainv[i+1] * (i+1) % P
inv = [0] * (2*v+2)
for i in range(1, 2*v+2):
    inv[i] = fainv[i] * fa[i-1] % P

T = create_table(v)
C = lambda n, k: fact(n, T) * pow(fact(k, T) * fact(n-k, T), P-2, P) % P
 
N, M = map(int, input().split())
X = list(map(int, input().split()))

R = 0
for i in range(N):
    R = (R + X[i]*C(i+M, i)*C(N-i+M-1, N-i-1)) % P
print(R)