A company has n employees numbered from 1 to n. Each employee either has no immediate manager or exactly one immediate manager, who is another employee with a different number. An employee A is said to be the superior of another employee B if at least one of the following is true:

  * Employee A is the immediate manager of employee B
  * Employee B has an immediate manager employee C such that employee A is the superior of employee C. 



The company will not have a managerial cycle. That is, there will not exist an employee who is the superior of his/her own immediate manager.

Today the company is going to arrange a party. This involves dividing all n employees into several groups: every employee must belong to exactly one group. Furthermore, within any single group, there must not be two employees A and B such that A is the superior of B.

What is the minimum number of groups that must be formed?

Input

The first line contains integer n (1 ≤ n ≤ 2000) — the number of employees.

The next n lines contain the integers pi (1 ≤ pi ≤ n or pi = -1). Every pi denotes the immediate manager for the i-th employee. If pi is -1, that means that the i-th employee does not have an immediate manager. 

It is guaranteed, that no employee will be the immediate manager of him/herself (pi ≠ i). Also, there will be no managerial cycles.

Output

Print a single integer denoting the minimum number of groups that will be formed in the party.

Examples

Input

5
-1
1
2
1
-1


Output

3

Note

For the first example, three groups are sufficient, for example: 

  * Employee 1 
  * Employees 2 and 4 
  * Employees 3 and 5 
import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.io.OutputStream;
import java.io.InputStreamReader;
import java.io.FileNotFoundException;
import java.io.File;
import java.util.StringTokenizer;
import java.io.Writer;
import java.io.BufferedReader;
import java.io.UnsupportedEncodingException;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 *
 * @author MaxHeap
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        FastReader in = new FastReader(inputStream);
        OutputWriter out = new OutputWriter(outputStream);
        Party solver = new Party();
        solver.solve(1, in, out);
        out.close();
    }

    static class Party {
        public void solve(int testNumber, FastReader in, OutputWriter out) {
            int n = in.nextInt();
            int[] parent = new int[n + 1];
            for (int i = 0; i < n; i++) {
                parent[i] = in.nextInt();
                if (parent[i] > 0) --parent[i];
            }
            int ans = 1;
            for (int i = 0; i < n; i++) {
                int d = 1;
                for (int x = i; parent[x] != -1; x = parent[x], d++) ;
                ans = Math.max(ans, d);
            }
            out.println(ans);
        }

    }

    static class FastReader {
        BufferedReader reader;
        StringTokenizer st;

        public FastReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream));
            st = null;
        }

        public String next() {
            while (st == null || !st.hasMoreTokens()) {
                try {
                    String line = reader.readLine();
                    if (line == null) {
                        return null;
                    }
                    st = new StringTokenizer(line);
                } catch (Exception e) {
                    throw new RuntimeException();
                }
            }
            return st.nextToken();
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

    }

    static class OutputWriter extends PrintWriter {
        public OutputWriter(OutputStream os, boolean autoFlush) {
            super(os, autoFlush);
        }

        public OutputWriter(Writer out) {
            super(out);
        }

        public OutputWriter(Writer out, boolean autoFlush) {
            super(out, autoFlush);
        }

        public OutputWriter(String fileName) throws FileNotFoundException {
            super(fileName);
        }

        public OutputWriter(String fileName, String csn) throws FileNotFoundException, UnsupportedEncodingException {
            super(fileName, csn);
        }

        public OutputWriter(File file) throws FileNotFoundException {
            super(file);
        }

        public OutputWriter(File file, String csn) throws FileNotFoundException, UnsupportedEncodingException {
            super(file, csn);
        }

        public OutputWriter(OutputStream out) {
            super(out);
        }


        public void flush() {
            super.flush();
        }


        public void close() {
            super.close();
        }

    }
}

