from itertools import accumulate

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

accA = list(accumulate(A, lambda a, b: a * b))

ans = 0

for i in range(N - 1):
    ans += accA[i] * pow(3, N - i - 2, MOD) * 2
    ans %= MOD
ans += accA[-1]
ans %= MOD
print(ans)