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.util.*;

public class C implements Runnable {
    int a[ ];

    public void solve( ) throws Throwable {
        int n = in.nextInt( );
        a = new int[ n ];
        for ( int i = 0; i < n; ++i ) {
            a[ i ] = in.nextInt( );
        }
        int max = 0;
        for ( int i = 0; i < n; ++i ) {
            max = Math.max( deep( i, 0 ), max );
        }
        out.println( max );
    }

    public int deep( int i, int level ) {
        if ( a[ i ] < 0 ) {
            return level + 1;
        }
        return deep( a[ i ] - 1, level + 1 );
    }

    

    public void run( ) {
        in = new FastScanner( System.in );
        out = new PrintWriter( new PrintStream( System.out ), true );

        try {
            solve( );
            out.close( );
            System.exit( 0 );
        } catch( Throwable e ) {
            e.printStackTrace( );
            System.exit( -1 ); 
        }
    }


    public void debug( Object...os ) {
        System.err.println( Arrays.deepToString( os ) );
    }

    public static void main( String[ ] args ) {
        new Thread( new C( ) ).start( );
    }



    private FastScanner in;
    private PrintWriter out;

    private static class FastScanner {
        private int charsRead;
        private int currentRead;
        private byte buffer[ ] = new byte[ 0x1000 ];
        private InputStream reader;

        public FastScanner( InputStream in ) {
            reader = in;
        }

        public int read( ) {
            if ( currentRead == -1 ) {
                throw  new InputMismatchException( );
            }

            if ( currentRead >= charsRead ) {
                currentRead = 0;
                try {
                    charsRead = reader.read( buffer );

                } catch( IOException e ) {
                    throw new InputMismatchException(  );
                }

                if ( charsRead <= 0 ) {
                    return -1;
                }
            }

            return buffer[ currentRead++ ];
        }

        public int nextInt( ) {
            int c = read( );

            while ( isWhitespace( c ) ) {
                c = read( );
            }

            if ( c == -1 ) {
                throw new NullPointerException( );
            } 

            if ( c != '-' && !( c >= '0' && c <= '9' ) ) {
                throw new InputMismatchException( );
            }

            int sign = c == '-' ? -1 : 1;
            if ( sign == -1 ) {
                c = read( );
            }

            if ( c == -1 || !( c >= '0' && c <= '9' ) ) {
                throw new InputMismatchException( );
            }

            int ans = 0;
            while ( !isWhitespace( c )  && c != -1 ) {
                if ( !( c >= '0' && c <= '9' ) ) {
                    throw  new InputMismatchException( );
                }
                int num = c - '0';
                ans = ans * 10 + num;
                c = read( );
            }

            return ans * sign;
        }

        public long nextLong( ) {
            int c = read( );

            while ( isWhitespace( c ) ) {
                c = read( );
            }

            if ( c == -1 ) {
                throw new NullPointerException( );
            }

            if ( c != '-' && !( c >= '0' && c <= '9' ) ) {
                throw new InputMismatchException( );
            }

            int sign = c == '-' ? -1 : 1;
            if ( sign == -1 ) {
                c = read( );
            }

            if ( c == -1 || !( c >= '0' && c <= '9' ) ) {
                throw new InputMismatchException( );
            }

            long ans = 0;
            while ( !isWhitespace( c )  && c != -1 ) {
                if ( !( c >= '0' && c <= '9' ) ) {
                    throw  new InputMismatchException( );
                }
                int num = c - '0';
                ans = ans * 10 + num;
                c = read( );
            }

            return ans * sign;
        }



        public boolean isWhitespace( int c ) {
            return  c == ' ' || c == '\t' || c == '\n' || c == '\r' || c == -1;
        }

        public String next( ) {
            int c = read( );
            StringBuffer ans = new StringBuffer( );

            while ( isWhitespace( c ) && c != -1 ) {
                c  = read( );
            }

            if ( c == -1 ) {
                return null;
            }

            while ( !isWhitespace( c ) && c != -1 ) {
                ans.appendCodePoint( c );
                c = read( );
            }

            return ans.toString( );

        }

               
        public String nextLine( ) {
            String ans = nextLine0( );

            while ( ans.trim( ).length( ) == 0 ) {
                ans = nextLine0( );
            }

            return ans;
        }
        
        private String nextLine0( ) {
            int c = read( );
            if ( c == -1 ) {
                return null;
            }
            StringBuffer ans = new StringBuffer( );
            while ( c != '\n' && c != '\r' && c != -1 ) {
                ans.appendCodePoint( c );
                c = read( );
            }

            return ans.toString( );

        }


       
        public double nextDouble( ) {
            int c = read( );
            while ( isWhitespace( c ) ) {
                c = read( );
            }

            if ( c == -1 ) {
                throw new NullPointerException( ); 
            }

            if ( c != '.' && c != '-' && !( c >= '0' && c <= '9' ) ) {
                throw new InputMismatchException( );
            }

            int sign = c == '-' ? -1 : 1;

            double ans = 0;
            while ( c != -1 && c != '.' && !isWhitespace( c ) ) {
                if ( !( c >= '0' && c <= '9' ) ) {
                    throw new InputMismatchException( );
                }

                int num = c - '0'; 
                ans = ans * 10.0 + num;
                c = read( );
            }

            if ( !isWhitespace( c ) && c != -1 && c != '.' ) {
                throw new InputMismatchException( );
            }

            double pow10 = 1.0;

            if ( c == '.' ) {
                c = read( );
            }

            while ( !isWhitespace( c ) && c != -1 ) {
                pow10 *= 10.0;

                if ( !( c >= '0' && c <= '9' ) ) {
                    throw new InputMismatchException( );
                }
                int num = c - '0';
                ans = ans * 10.0 + num; 
                c = read( );
            }

            return ans * sign / pow10;
        }
    }

}
