Long Path

1000ms

262144K

Description:

One day, little Vasya found himself in a maze consisting of (n + 1) rooms, numbered from 1 to (n + 1). Initially, Vasya is at the first room and to get out of the maze, he needs to get to the (n + 1)-th one.

The maze is organized as follows. Each room of the maze has two one-way portals. Let's consider room number i (1 ≤ i ≤ n), someone can use the first portal to move from it to room number (i + 1), also someone can use the second portal to move from it to room number p_i, where 1 ≤ p_i ≤ i.

In order not to get lost, Vasya decided to act as follows.

Each time Vasya enters some room, he paints a cross on its ceiling. Initially, Vasya paints a cross at the ceiling of room 1.
Let's assume that Vasya is in room i and has already painted a cross on its ceiling. Then, if the ceiling now contains an odd number of crosses, Vasya uses the second portal (it leads to room p_i), otherwise Vasya uses the first portal.

Help Vasya determine the number of times he needs to use portals to get to room (n + 1) in the end.

Input:

The first line contains integer n (1 ≤ n ≤ 10³) — the number of rooms. The second line contains n integers p_i (1 ≤ p_i ≤ i). Each p_i denotes the number of the room, that someone can reach, if he will use the second portal in the i-th room.

Output:

Print a single number — the number of portal moves the boy needs to go out of the maze. As the number can be rather large, print it modulo 1000000007 (10⁹ + 7).

Sample Input:

2
1 2

Sample Output:

Sample Input:

4
1 1 2 3

Sample Output:

Sample Input:

5
1 1 1 1 1

Sample Output:

Informação

Provedor Codeforces

Código CF407B