public class Main {
    public static int max = 0;//结果
    public static int x;//数组大小
    public static boolean[] b;//判断数组
    public static int[] array;//数组记录
    public static int start;
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        x = scan.nextInt();
        b = new boolean[x+1];
        array = new int[x+1];
        for(int i = 1;i<=x;i++) array[i] = scan.nextInt();
        for(int i = 1;i<=x;i++)
        {
            start = i;
            dfs(i,0);
        }
        System.out.println(max);
        scan.close();
    }
    public static void dfs(int n,int size)//终止位置,尺寸
    {
        if(b[n])
        {
            if(start == n && max<size)//起始与终止指向一个人
            {
                max = size;
            }
            return;
        }
        if(b[n]==false)//说明这个结点没有被访问过
        {
            b[n] = true;
            dfs(array[n],size+1);
            b[n] = false;//进行回溯
        }
    }
}