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.*;
import java.lang.*;
import java.util.*;
import java.math.*;

class Main {
	static BufferedReader jvin = new BufferedReader(new InputStreamReader(System.in));
	static PrintWriter jvout = new PrintWriter(System.out);

	static int maxN = (int)1E5+5;
	int n;
	int[] a;

	public static void main(String[] args) throws IOException {
		Main instance = new Main();
		instance.passStaticVar();
	}

	public void passStaticVar() throws IOException {
		n = Integer.parseInt(jvin.readLine());
		a = new int[n+1];
		for (int i = 1; i <= n; ++i) 
			a[i] = Integer.parseInt(jvin.readLine());
		
		boolean[] marked = new boolean[n+1];
		for (int i = 1; i <= n; ++i)
			marked[i] = false;
		int result = 0, i = 1;
		for ( ; !marked[i] && i != 2; i = a[i]) {
			marked[i] = true;
			++result;
		}
		if (i == 2) jvout.println(result);
		else jvout.println("-1");
		jvout.flush();
	}
}