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

func main() {
  var n int
  fmt.Scan(&n)
  a := readLineNums(n)
  b := make([]bool, n)
  b[0] = true
  k := 0
  ok := false
  ans := 0
  for {
    ans += 1
    k = a[k] - 1
    if k == 1 {
      ok = true
      break
    }
    if b[k] {
      break
    }
    b[k] = true
  }
  if ok {
    fmt.Print(ans)
  } else {
    fmt.Print(-1)
  }
}

var sc = bufio.NewScanner(os.Stdin)
func nextLine() string {
    sc.Scan()
    return sc.Text()
}

func readLineNums(len int) (nums []int){
    for i:=0; i<len; i++{
        tmp,_ := strconv.Atoi(nextLine())
        nums = append(nums,tmp)
    }
    return
}