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: Wrong Answer)

package main

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

////////////////////////////////////////
///        templates                 ///
////////////////////////////////////////

var sc = bufio.NewScanner(os.Stdin)

func nextLine() string {
	sc.Scan()
	return sc.Text()
}

var rdr = bufio.NewReaderSize(os.Stdin, 1000000)

func readBigLine() string {
	buf := make([]byte, 0, 1000000)
	for {
		l, p, e := rdr.ReadLine()
		if e != nil {
			panic(e)
		}
		buf = append(buf, l...)
		if !p {
			break
		}
	}
	return string(buf)
}

func strSprit(str string) []string {
	cols := strings.Split(str, " ")
	return cols
}

func parseInt(str string) int {
	n, _ := strconv.Atoi(str)
	return n
}

func intSprit(str string) []int {
	strs := strSprit(str)
	cols := make([]int, len(strs))
	for i, v := range strs {
		cols[i] = parseInt(v)
	}
	return cols
}

type SortSlice []int

func (s SortSlice) Len() int {
	return len(s)
}

func (s SortSlice) Swap(i, j int) {
	s[i], s[j] = s[j], s[i]
}

func (s SortSlice) Less(i, j int) bool {
	return s[i] < s[j]
}

func reverseString(str string) string {
	buf := []rune(str)
	for i, j := 0, len(buf)-1; i < j; i, j = i+1, j-1 {
		buf[i], buf[j] = buf[j], buf[i]
	}
	return string(buf)
}

////////////////////////////////////////
///        end templates             ///
////////////////////////////////////////

func main() {
	line := readBigLine()
	N := parseInt(line)

	a := make([]int, N+1)
	for i := 1; i <= N; i++ {
		line = nextLine()
		a[i] = parseInt(line)
	}

	count := 1
	index := a[1]
	for count < N {
		count++
		if a[index] == 2 {
			fmt.Println(count)
			return
		} else {
			index = a[index]
		}
	}

	fmt.Println(-1)

}