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 (GCC 9.2.1) (judge verdict: Wrong Answer)

#include<stdio.h>
int main()
{
int n,i,min,cc,temp,ansz,kk; //anszは暫定のans,kkは2を通らずループするスタート地点の個数
  //ccはforループ内でのスイッチで1は2にたどり着いたことを、2はループすることを示す。
  ansz=0;
  cc=0;
  kk=0;
  min=100001;
  scanf("%d",&n);
  
  int sw[n],th[n];
  
  for(i=0;i<n;++i)
  {
  scanf("%d",&sw[i]);
   th[i]=0;
  }
  
  for(i=0;i<n;++i)
  {temp=sw[i]; //スタートをiで定める
  while(cc==0)
    {
    th[temp-1]++;
    if(th[temp-1]==2) cc=2;
    temp=sw[temp-1];
    ansz++;
    if(temp=2)  cc=1;
    }
  if(cc=1 && ansz < min) min=ansz;
  if(cc=2) kk++;
   ansz=0;
   cc=0; //ccのリセット
  }
  
  if(kk=n) printf("-1");
  else printf("%d",min);
  
return 0;
}