Kostya likes Codeforces contests very much. However, he is very disappointed that his solutions are frequently hacked. That's why he decided to obfuscate (intentionally make less readable) his code before upcoming contest.

To obfuscate the code, Kostya first looks at the first variable name used in his program and replaces all its occurrences with a single symbol a, then he looks at the second variable name that has not been replaced yet, and replaces all its occurrences with b, and so on. Kostya is well-mannered, so he doesn't use any one-letter names before obfuscation. Moreover, there are at most 26 unique identifiers in his programs.

You are given a list of identifiers of some program with removed spaces and line breaks. Check if this program can be a result of Kostya's obfuscation.

Input

In the only line of input there is a string S of lowercase English letters (1 ≤ |S| ≤ 500) — the identifiers of a program with removed whitespace characters.

Output

If this program can be a result of Kostya's obfuscation, print "YES" (without quotes), otherwise print "NO".

Examples

Input

abacaba


Output

YES


Input

jinotega


Output

NO

Note

In the first sample case, one possible list of identifiers would be "number string number character number string number". Here how Kostya would obfuscate the program:

  * replace all occurences of number with a, the result would be "a string a character a string a",
  * replace all occurences of string with b, the result would be "a b a character a b a",
  * replace all occurences of character with c, the result would be "a b a c a b a",
  * all identifiers have been replaced, thus the obfuscation is finished.
//package main;

import java.io.*;
import java.util.*;
//import java.math.BigInteger;


public class Main {
    public void solve( ) throws Throwable {
        char[] a=in.nextLine().toCharArray();
        boolean[] f=new boolean[26];
        Arrays.fill(f, false);
        int l=a.length;
        LinkedList<Character> q=new LinkedList(); 
        for(int i=0;i<l;i++){
            if(!f[a[i]-'a']){
                f[a[i]-'a']=true;
                q.add(a[i]);
            }
            else{
                a[i]='#';
            }
        }
        boolean flag=false;
        for(int i=0;!q.isEmpty();i++){
            char t=q.poll();
            if(t!=('a'+i)){
                flag=true;
                break;
            }
        }
        if(!flag)
            out.println("YES");
        else
            out.println("NO");
    }
    
//BIT    
//    int read(int idx){
//        if(idx==0)
//            return 0;
//        int sum=0;
//        while(idx>0){
//            sum=(sum+tree[idx]%1000000007)%1000000007;            
//            idx-=(idx&-idx);
//        }
//        return sum;
//    }
//    
//    void update(int idx, int val){
//        while(idx<=(v+1)){
//            tree[idx]=(val%1000000007+tree[idx]%1000000007)%1000000007;
//            idx+=(idx&-idx);
//        }
//    }
    
//    boolean check(int i, int j){
//        if((i>-1&&i<4)&&(j>-1&&j<4))
//            return true;
//        else
//            return false;
//    }
//    int bs(int level, double mi, double tg){
//        if(level==1)
//            return 1;
//        if(tg==mi)
//            return level;
//        if(tg<mi)
//            return bs(level-1, Math.pow(2, level-2), tg);
//        else
//            return bs(level-1, Math.pow(2, level-2), tg-mi);
//            
//    }
    
//    void sieve(){
//        Arrays.fill(mark, false);
//        int limit=(int)Math.sqrt(100000)+2;
//        mark[0]=mark[1]=true;
//        for(int i=4;i<=100000;i+=2){
//            mark[i]=true;
//        }
//        for(int i=3; i<=100000;i+=2){
//            if(!mark[i]){
//                if(i<=limit){
//                    for(int j=i*i;j<=100000;j+=i*2){
//                        mark[j]=true;
//                    }
//                }
//            }
//        }
//    }
    
    
//    class car implements Comparable<car>{
//        public int c, v;
//        @Override
//        public int compareTo(car x){
//            return this.c-x.c;
//        }
//    }
    
    
    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 Main( ) ).run( );
    }

    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 ( charsRead == -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 || c=='(' || c==')';
        }

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

}