n = int(input())
A = list(map(int, input().split()))
mod = 10**9 + 7

ans = 0
curr = 1
for i in range(n):
    curr *= A[i]
    curr %= mod
    if i < n - 1:
        ans += curr * 2 * pow(3, n - i - 2, mod) % mod
    else:
        ans += curr
    ans %= mod
print(ans)