|Codeforces Round #239 (Div. 1)|
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.
Help Vasya determine the number of times he needs to use portals to get to room (n + 1) in the end.
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.
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).
1 1 2 3
1 1 1 1 1