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 Go (1.6) (judge verdict: Accepted)

package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

func main() {
	n := getInt()
	as := make([]int, n)
	for i := range as {
		as[i] = getInt()
	}

	flags := make([]bool, n)
	ans := 0
	i := 0
	for {
		if flags[i] == true {
			ans = -1
			break
		} else if i == 1 {
			break
		}
		flags[i] = true
		i = as[i] - 1
		ans++
	}

	fmt.Println(ans)
}

// -----------------------------------------

var scanner = wordScanner()

func wordScanner() *bufio.Scanner {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	return sc
}

func getInt() int {
	scanner.Scan()
	i, err := strconv.Atoi(scanner.Text())
	if err != nil {
		panic(err)
	}
	return i
}

func getString() string {
	scanner.Scan()
	s := scanner.Text()
	return s
}