mod = 10**9+7
n, *A = map(int, open(0).read().split())
ans = 0
t = 1
L = [1, 2]
for _ in range(n-2):
    L.append(L[-1] * 3 % mod)
for i in range(n):
    t = t*A[i]%mod
    ans += t*L[~i]
    ans %= mod
print(ans)