n = int(input())
seql = list(map(int, input().split()))
n -= 2
ans = 0
z = 10**9+7
for i in range(n+1):
    p = seql[i]
    if not p:
        break
    seql[i+1] = seql[i+1]*p%z
    ans = (ans+pow(3, n, z)*2*p)%z
    n -= 1
else:
    ans += seql[-1]
print (ans%z)