mod = int(1e9+7)
n = int(input())
mul = 1
ans = 0
for i,a in enumerate(list(map(int,input().split()))):
	mul = (mul * a) % mod
	if i == n-1:
		ans += mul
	else:
		ans += mul * 2 * pow(3,n-2-i,mod) 
	ans %= mod
print(ans)