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++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <bits/stdc++.h>

#define DEBUG(C) cerr << #C << " = " << C << endl

using namespace std;

const int MAX = 1e5 + 10;
int n, a[MAX];

bool r[MAX], u[MAX];

int main() {
	cin >> n;
	for (int i = 0; i < n; i++) {
		cin >> a[i];
		a[i]--;
	}
	r[0] = u[0] = true;
	int now = 0;
	int cnt = 0;
	while (!u[a[now]]) {
		++cnt;
		now = a[now];
		if (a[now] == 1) {
			cout << cnt + 1 << endl;
			return 0;
		}
		r[now] = u[now] = true;
	}
	cout << -1 << endl;
  return 0;
}