n = int(input())
seql = list(map(int, input().split()))
import operator, itertools

z = 10**9+7
n -= 2 
ans = 0
for p in itertools.accumulate(seql, func=operator.mul):
    ans = ans%z + (p * 3**n * 2)%z if n >= 0 else (ans+p)%z
    n -= 1
print (ans)