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

inv = [0] * 4
inv[1] = 1
inv[2] = P - P // 2
inv[3] = P - P // 3 * inv[P % 3] % P
c = 1
for _ in range(N-2):
    c *= 3
    c %= P

now = A[0] * 2 * c % P
s = now
for i in range(2,N):
    now = now * inv[3] * A[i-1] % P
    s += now
    s %= P
now = now * inv[2] * A[N-1] % P
s += now
s %= P
print(s)