N = int(input())
l = list(map(int, input().split()))
md = 1000000007

t = 1
beki = []
for i in range(N):
	beki.append(t)
	t *= 3

p = l[0]
ans = 0
for i in range(N-1):
	ans += (2 * beki[N-i-2] * p) 
	p *= l[i+1]

ans += p

print(ans%md)