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 C (GCC 5.4.1) (judge verdict: Wrong Answer)

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<math.h>

int main()
{
	int n;
	int i;
	scanf("%d", &n);

	int *a = (int*)malloc(n * sizeof(int));
	int *b = (int*)malloc(n * sizeof(int));
	b[0] = 1;

	for (i = 0; i < n; i++) {
		scanf("%d", &a[i]);
	}

	int bsize = 1;
	int k = 0;
	int count = 0;
	int ans=-1;
	
	while (bsize < n) {
		int d = a[k];
		if (d == 2) {
			ans = 0;
			break;
		}
		else {
			for (int j = 0; j < bsize; j++) {
				if (d == b[j]) {
					ans = -1;
				}
			}
			b[bsize] = d;
		}
		k = d-1;
		count++;
		bsize++;
	}
	
	if (ans == 0)printf("%d\n", count);
	else printf("%d\n", -1);
	return 0;
}