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: Accepted)

#include <stdio.h>

int main(void) {
	int N;
	int *a;
	int i, check = -1, num = 2, x, ans = 0;
	int *c;

	scanf("%d", &N);
	a = (int*)malloc(sizeof(int)*N);
	c = (int*)malloc(sizeof(int)*N);
	for (i = 0; i < N; i++) {
		scanf("%d", &a[i]);
		if (a[i] == 2) check = 1;
		c[i] = 0;
	}
	if (check!=1) {
		printf("%d\n", check);
		return 0;
	}
	i = 0;
	while (c[i] == 0) {
		num = a[i];
		c[i] = 1;
		i = num - 1;
		ans++;
		if (num == 2) {
			printf("%d\n", ans);
			return 0;
		}
	}
	printf("-1\n");

	return 0;
}