Problem2878--Long Path

2878: Long Path

Time Limit: 2 Sec  Memory Limit: 256 MB
Submit: 0  Solved: 0
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Description

time limit per test
1 second
memory limit per test
256 megabytes
input
standard input
output
standard output

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 pi, where 1≤pi≤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 pi), 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 pi (1≤pi≤i). Each pi 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).

Examples
Input
2
1 2
Output
4
Input
4
1 1 2 3
Output
20
Input
5
1 1 1 1 1
Output
62

Source/Category

 
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