Problem:
Score : 200 points

Problem Statement

Takahashi wants to gain muscle, and decides to work out at AtCoder Gym.

The exercise machine at the gym has N buttons, and exactly one of the buttons is lighten up.
These buttons are numbered 1 through N.
When Button i is lighten up and you press it, the light is turned off, and then Button a_i will be lighten up. It is possible that i=a_i.
When Button i is not lighten up, nothing will happen by pressing it.

Initially, Button 1 is lighten up. Takahashi wants to quit pressing buttons when Button 2 is lighten up.

Determine whether this is possible. If the answer is positive, find the minimum number of times he needs to press buttons.

Constraints

2 ≤ N ≤ 10^5

1 ≤ a_i ≤ N

Input

Input is given from Standard Input in the following format:

N
a_1
a_2
:
a_N

Output

Print -1 if it is impossible to lighten up Button 2.
Otherwise, print the minimum number of times we need to press buttons in order to lighten up Button 2.

Sample Input 1

3
3
1
2

Sample Output 1

2

Press Button 1, then Button 3.

Sample Input 2

4
3
4
1
2

Sample Output 2

-1

Pressing Button 1 lightens up Button 3, and vice versa, so Button 2 will never be lighten up.

Sample Input 3

5
3
3
4
2
4

Sample Output 3

3

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.io.InputStream;
import java.util.Scanner;

public class Main {
	static Scanner sc;

	public static void main(String[] args) throws Exception {
		//InputStream in = new FileInputStream("src/input.txt");
		InputStream in = System.in;

		sc = new Scanner(in);
		
		int n = sc.nextInt();
		
		int[] a = new int[n];
		
		for(int i = 0; i < n; i++){
			a[i] = sc.nextInt() - 1;
		}
		
		int answer = 0;
		int nowPoint = 0;
		
		while(nowPoint + 1 != 2){
			int prePoint = nowPoint;
			nowPoint = a[nowPoint] ;
			a[prePoint] = -1;
			answer++;
			//System.out.println("ans " + answer);
			if(nowPoint == -1){
				answer = -1;
				break;
				//System.out.println("out");
			}
		}
		
		System.out.println(answer);

	}
}