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.*;
    import java.text.*;
    import java.util.*;
    import java.util.regex.*;

    public class Main{
        static class Run implements Runnable{
            //TODO parameters
            final boolean consoleIO = true;
            final String inFile = "input.txt";
            final String outFile = "output.txt";
            
            int n;
            int[] t;
            
            void read() {
                n = nextInt();
                t = new int[n];
                Arrays.fill(t, -1);
                
                for(int i = 0; i < n; ++i) {
                    int a = nextInt();
                    if(a != -1) {
                        t[i]= a - 1;
                    }
                }
            }
            
            int depth = 0;
            boolean[] v;
            
            void dfs(int s, int d) {
                if(s == -1)
                    return;
                
                v[s] = true;
                depth = Math.max(depth, d);
                
                dfs(t[s], d+1);
            }
            
            @Override
            public void run() {
                //TODO code
                read();
                v = new boolean[n];
                
                for(int i = 0; i < n; ++i) {
                    if(!v[i])
                        dfs(i, 0);
                }
                
                print(depth + 1);
                close();
            }
        //=========================================================================================================================
            BufferedReader in;
            PrintWriter out;
            StringTokenizer strTok;
           
            Run() {
                if (consoleIO) {
                    initConsoleIO();
                }
                else {
                    initFileIO();
                }
            }
           
            void initConsoleIO() {
                in = new BufferedReader(new InputStreamReader(System.in));
                out = new PrintWriter(new OutputStreamWriter(System.out));
            }
           
            void initFileIO() {
                try {
                    in = new BufferedReader(new FileReader(inFile));
                    out = new PrintWriter(new FileWriter(outFile));
                } catch (FileNotFoundException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
           
            void close() {
                try {
                    in.close();
                    out.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
           
            int nextInt() {
                return Integer.parseInt(nextToken());
            }
           
            double nextDouble() {
                return Double.parseDouble(nextToken());
            }
           
            float nextFloat() {
                return Float.parseFloat(nextToken());
            }
           
            long nextLong() {
                return Long.parseLong(nextToken());
            }
           
            String nextLine() {
                try {
                    return in.readLine();
                } catch (IOException e) {
                    return "__NULL";
                }
            }
           
            boolean hasMoreTokens() {
                return (strTok == null) || (strTok.hasMoreTokens());
            }
           
            String nextToken() {
                while (strTok == null || !strTok.hasMoreTokens()) {
                    String line;
                    try {
                        line = in.readLine();
                        strTok = new StringTokenizer(line);
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
               
                return strTok.nextToken();
            }
           
            void cout(Object o){
                System.out.println(o);
            }
           
            void print(Object o) {
                out.write(o.toString());
            }
           
            void printf(String format, Object... args) {
                out.printf(format, args);
            }
           
            String sprintf(String format, Object... args) {
            return MessageFormat.format(format, args);
        }
        }
       
        static class Pair<A, B> {
            A a;
            B b;
           
            A f() {
                return a;
            }
           
            B s() {
                return b;
            }
           
            Pair(A a, B b) {
                this.a = a;
                this.b = b;
            }
           
            Pair(Pair<A, B> p) {
                a = p.f();
                b = p.s();
            }
        }
       
        public static void main(String[] args) throws IOException {
            Run run = new Run();
            Thread thread = new Thread(run);
            thread.run();
        }
    }