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 Rust (1.15.1) (judge verdict: Accepted)

mod reader {
    use std::fmt::Debug;
    use std::str::FromStr;
    use std::collections::VecDeque;
    use std::io::{self, Read};

    fn _read_line() -> String {
        let mut buf = String::new();
        io::stdin().read_to_string(&mut buf);
        buf
    }

    fn _read_vec_deque_string() -> VecDeque<String> {
        _read_line().split_whitespace().map(|s| s.to_string()).collect()
    }

    pub struct Reader {
        buf : VecDeque<String>
    }

    impl Reader {
        pub fn new() -> Reader {
            Reader {buf : VecDeque::new()}
        }

        fn update_buf(&mut self) {
            if self.buf.is_empty() {
                self.buf = _read_vec_deque_string();
            }
        }

        pub fn next<T>(&mut self) -> T where T: FromStr, T::Err: Debug {
            self.update_buf();
            self.buf.pop_front().unwrap().parse::<T>().unwrap()
        }
    }
}


fn main() {
    let mut reader = reader::Reader::new();

    const N : usize = 100000;
    let mut array: [i32; N] = [0; N];

    let n : usize = reader.next();
    for i in 0..n {
        array[i] = reader.next::<i32>() - 1;        
    }

    let mut cnt = 0;
    let mut idx = 0;
    while idx >= 0 && idx != 1{
        let prv : usize = idx as usize;
        idx = array[prv];
        array[prv] = -1;
        cnt += 1;
    }

    println!("{}", if idx == 1 {
        cnt
    } else {
        idx
    });
}