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 5.4.1) (judge verdict: Time Limit Exceeded)

#include<stdio.h>

int main(){
    int n,A[100000] = {0};
    int B[100000] = {0};

    scanf("%d",&n);

    for(int i = 1; i < n+1; i++){
        scanf("%d",&A[i]);
    }

    int ans = 0;
    int i = 1;
    B[i] = i;
    while (1)
    {
        i = A[i];
        int j = 1;
        int flag = 0;
        while (B[j] != 0)
        {
            if(i == B[j]){ 
                flag = 1;
                break;
            }
            j++;
        }
        B[j] = i;
        if(flag){
            ans = -1;
            break;
        } 
        ans++;
        if(i == 2) break;
    }

    printf("%d\n",ans);
    

}