n = int(input())
cur = 1
a = list(map(int, input().split()))
ans = 0
mod = 10 ** 9 + 7
for i in range(n):
	cur *= a[i]
	cur %= mod
	if i == n - 1: ans += cur
	else: ans += cur * 2 * pow(3, n - i - 2, mod)
	ans %= mod
print(ans)