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>
int main()
{
	int a[100001]={};
	int b[100001]={};
	int n;
	scanf("%d",&n);
	for(int k=1;k<=n;k++)
	{
		scanf("%d",&a[k]);
	}
	int i=a[1];
	int j=1;
	if(a[1]==2)
	{
		printf("1");
		return 0;
	}
	for(;;)
	{
		b[a[i]]=1;
		i=a[i];
		j++;
		if(i==2)
		{
			break;
		}
		if(i==a[i])
		{
			printf("-1");
			return 0;
		}
		if(b[i]==1)
		{
			printf("-1");
			return 0;
		}
	}
	printf("%d",j);
	return 0;
}