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.
import java.io.File;import java.io.FileInputStream;import java.io.FileNotFoundException;
import java.io.IOException;import java.io.InputStream;import java.io.PrintStream;
import java.io.PrintWriter;import java.security.AccessControlException;import java.util.Arrays;
import java.util.Collection;import java.util.Comparator;import java.util.List;import java.util.Map;
import java.util.Objects;import java.util.TreeMap;import java.util.function.Function;
import java.util.stream.Collectors;import java.util.stream.IntStream;import java.util.stream.LongStream;
import java.util.stream.Stream;public class _p000765B {static public void main(final String[] args) 
throws IOException{p000765B._main(args);}
static private class p000765B extends Solver{public p000765B(){singleTest=true;}
@Override public void solve()throws IOException{int[]S=lineToCharArray();int next
='a';boolean res=true;for(int i=0;i<S.length;i++){if(S[i]>next){res=false;break;
}else if(S[i]==next){next++;}}pw.println(yesNo(res));}static public void _main(String[]
args)throws IOException{new p000765B().run();}}static private class MyScanner{private 
StringBuilder cache=new StringBuilder();int cache_pos=0;private int first_linebreak
=-1;private int second_linebreak=-1;private StringBuilder sb=new StringBuilder();
private InputStream is=null;public MyScanner(final InputStream is){this.is=is;}private 
String charToString(final int c){return String.format("'%s'",c=='\n'?"\\n":(c=='\r'
?"\\r":String.valueOf((char)c)));}public int get(){int res=-1;if(cache_pos<cache.length())
{res=cache.charAt(cache_pos);cache_pos++;if(cache_pos==cache.length()){cache.delete(0,
cache_pos);cache_pos=0;}}else{try{res=is.read();}catch(IOException ex){throw new 
RuntimeException(ex);}}return res;}private void unget(final int c){if(cache_pos==
0){cache.insert(0,(char)c);}else{cache_pos--;}}public String nextLine(){sb.delete(0,
sb.length());int c;boolean done=false;boolean end=false;while((c=get())!=-1){if(check_linebreak(c))
{done=true;if(c==first_linebreak){if(!end){end=true;}else{cache.append((char)c);
break;}}else if(second_linebreak!=-1 && c==second_linebreak){break;}}if(end && c
!=first_linebreak && c!=second_linebreak){cache.append((char)c);break;}if(!done)
{sb.append((char)c);}}return sb.toString();}private boolean check_linebreak(int 
c){if(c=='\n'|| c=='\r'){if(first_linebreak==-1){first_linebreak=c;}else if(c!=first_linebreak 
&& second_linebreak==-1){second_linebreak=c;}return true;}return false;}public int 
nextInt(){return Integer.parseInt(next());}public long nextLong(){return Long.parseLong(next());
}public boolean hasNext(){boolean res=false;int c;while((c=get())!=-1){if(!check_linebreak(c)
&& c!=' '&& c!='\t'){res=true;unget(c);break;}}return res;}public String next(){
sb.delete(0,sb.length());boolean started=false;int c;while((c=get())!=-1){if(check_linebreak(c)
|| c==' '|| c=='\t'){if(started){unget(c);break;}}else{started=true;sb.append((char)c);
}}return sb.toString();}public int nextChar(){return get();}public boolean eof()
{int c=get();boolean res=false;if(c!=-1){unget(c);}else{res=true;}return res;}public 
double nextDouble(){return Double.parseDouble(next());}}static private class Pair<K,V>
{private K k;private V v;public Pair(final K t,final V u){this.k=t;this.v=u;}public 
K getKey(){return k;}public V getValue(){return v;}}static private abstract class 
Solver{protected String nameIn=null;protected String nameOut=null;protected boolean 
singleTest=false;protected boolean preprocessDebug=false;protected boolean doNotPreprocess
=false;protected PrintStream debugPrintStream=null;protected MyScanner sc=null;protected 
PrintWriter pw=null;final static String SPACE=" ";final static String SPACES="\\s+";
private int current_test=0;private int count_tests=0;protected int currentTest()
{return current_test;}protected int countTests(){return count_tests;}private void 
process()throws IOException{if(!singleTest){count_tests=lineToIntArray()[0];for(current_test
=1;current_test<=count_tests;current_test++){solve();pw.flush();}}else{count_tests
=1;current_test=1;solve();pw.flush();}}abstract protected void solve()throws IOException;
protected String[]lineToArray()throws IOException{return sc.nextLine().trim().split(SPACES);
}protected int[]lineToCharArray()throws IOException{return sc.nextLine().chars().toArray();
}protected int[]lineToIntArray()throws IOException{return Arrays.stream(lineToArray()).mapToInt(Integer::parseInt).toArray();
}protected long[]lineToLongArray()throws IOException{return Arrays.stream(lineToArray()).mapToLong(Long::parseLong).toArray();
}protected double[]lineToDoubleArray()throws IOException{return Arrays.stream(lineToArray()).mapToDouble(Double::parseDouble).toArray();
}protected void run()throws IOException{boolean done=false;try{if(nameIn!=null && 
new File(nameIn).exists()){try(FileInputStream fis=new FileInputStream(nameIn);PrintWriter 
pw0=select_output();){done=true;sc=new MyScanner(fis);pw=pw0;process();}}}catch(IOException 
ex){}catch(AccessControlException ex){}if(!done){try(PrintWriter pw0=select_output();
){sc=new MyScanner(System.in);pw=pw0;process();}}}private PrintWriter select_output()
throws FileNotFoundException{if(nameOut!=null){return new PrintWriter(nameOut);}
return new PrintWriter(System.out);}public static Map<Integer,Integer>mapc(final 
int[]a){return IntStream.range(0,a.length).collect(()->new TreeMap<Integer,Integer>(),
(res,i)->{res.put(a[i],res.getOrDefault(a[i],0)+1);},Map::putAll);}public static 
Map<Long,Integer>mapc(final long[]a){return IntStream.range(0,a.length).collect(
()->new TreeMap<Long,Integer>(),(res,i)->{res.put(a[i],res.getOrDefault(a[i],0)+
1);},Map::putAll);}public static<T>Map<T,Integer>mapc(final T[]a,Comparator<T>cmp)
{return IntStream.range(0,a.length).collect(cmp!=null?()->new TreeMap<T,Integer>(cmp)
:()->new TreeMap<T,Integer>(),(res,i)->{res.put(a[i],res.getOrDefault(a[i],0)+1);
},Map::putAll);}public static<T>Map<T,Integer>mapc(final T[]a){return mapc(a,null);
}public static Map<Integer,Integer>mapc(final IntStream a){return a.collect(()->
new TreeMap<Integer,Integer>(),(res,v)->{res.put(v,res.getOrDefault(v,0)+1);},Map::putAll
);}public static Map<Long,Integer>mapc(final LongStream a){return a.collect(()->
new TreeMap<Long,Integer>(),(res,v)->{res.put(v,res.getOrDefault(v,0)+1);},Map::putAll
);}public static<T>Map<T,Integer>mapc(final Stream<T>a,Comparator<T>cmp){return 
a.collect(cmp!=null?()->new TreeMap<T,Integer>(cmp):()->new TreeMap<T,Integer>(),
(res,v)->{res.put(v,res.getOrDefault(v,0)+1);},Map::putAll);}public static<T>Map<T,
Integer>mapc(final Stream<T>a){return mapc(a,null);}public static<T>Map<T,Integer>
mapc(final Collection<T>a,Comparator<T>cmp){return mapc(a.stream(),cmp);}public 
static<T>Map<T,Integer>mapc(final Collection<T>a){return mapc(a.stream());}public 
static Map<Integer,List<Integer>>mapi(final int[]a){return IntStream.range(0,a.length).collect(
()->new TreeMap<Integer,List<Integer>>(),(res,i)->{if(!res.containsKey(a[i])){res.put(a[i],
Stream.of(i).collect(Collectors.toList()));}else{res.get(a[i]).add(i);}},Map::putAll
);}public static Map<Long,List<Integer>>mapi(final long[]a){return IntStream.range(0,
a.length).collect(()->new TreeMap<Long,List<Integer>>(),(res,i)->{if(!res.containsKey(a[i]))
{res.put(a[i],Stream.of(i).collect(Collectors.toList()));}else{res.get(a[i]).add(i);
}},Map::putAll);}public static<T>Map<T,List<Integer>>mapi(final T[]a,Comparator<T>
cmp){return IntStream.range(0,a.length).collect(cmp!=null?()->new TreeMap<T,List<Integer>>(cmp)
:()->new TreeMap<T,List<Integer>>(),(res,i)->{if(!res.containsKey(a[i])){res.put(a[i],
Stream.of(i).collect(Collectors.toList()));}else{res.get(a[i]).add(i);}},Map::putAll
);}public static<T>Map<T,List<Integer>>mapi(final T[]a){return mapi(a,null);}public 
static Map<Integer,List<Integer>>mapi(final IntStream a){int[]i=new int[]{0};return 
a.collect(()->new TreeMap<Integer,List<Integer>>(),(res,v)->{if(!res.containsKey(v))
{res.put(v,Stream.of(i[0]).collect(Collectors.toList()));}else{res.get(v).add(i[0]);
}i[0]++;},Map::putAll);}public static Map<Long,List<Integer>>mapi(final LongStream 
a){int[]i=new int[]{0};return a.collect(()->new TreeMap<Long,List<Integer>>(),(res,
v)->{if(!res.containsKey(v)){res.put(v,Stream.of(i[0]).collect(Collectors.toList()));
}else{res.get(v).add(i[0]);}i[0]++;},Map::putAll);}public static<T>Map<T,List<Integer>>
mapi(final Stream<T>a,Comparator<T>cmp){int[]i=new int[]{0};return a.collect(cmp
!=null?()->new TreeMap<T,List<Integer>>(cmp):()->new TreeMap<T,List<Integer>>(),
(res,v)->{if(!res.containsKey(v)){res.put(v,Stream.of(i[0]).collect(Collectors.toList()));
}else{res.get(v).add(i[0]);}i[0]++;},Map::putAll);}public static<T>Map<T,List<Integer>>
mapi(final Stream<T>a){return mapi(a,null);}public static<T>Map<T,List<Integer>>
mapi(final Collection<T>a,Comparator<T>cmp){return mapi(a.stream(),cmp);}public 
static<T>Map<T,List<Integer>>mapi(final Collection<T>a){return mapi(a.stream());
}public static List<int[]>listi(final int[]a){return IntStream.range(0,a.length).mapToObj(i
->new int[]{a[i],i}).collect(Collectors.toList());}public static List<long[]>listi(final 
long[]a){return IntStream.range(0,a.length).mapToObj(i->new long[]{a[i],i}).collect(Collectors.toList());
}public static<T>List<Pair<T,Integer>>listi(final T[]a){return IntStream.range(0,
a.length).mapToObj(i->new Pair<T,Integer>(a[i],i)).collect(Collectors.toList());
}public static List<int[]>listi(final IntStream a){int[]i=new int[]{0};return a.mapToObj(v
->new int[]{v,i[0]++}).collect(Collectors.toList());}public static List<long[]>listi(final 
LongStream a){int[]i=new int[]{0};return a.mapToObj(v->new long[]{v,i[0]++}).collect(Collectors.toList());
}public static<T>List<Pair<T,Integer>>listi(final Stream<T>a){int[]i=new int[]{0};
return a.map(v->new Pair<T,Integer>(v,i[0]++)).collect(Collectors.toList());}public 
static<T>List<Pair<T,Integer>>listi(final Collection<T>a){int[]i=new int[]{0};return 
a.stream().map(v->new Pair<T,Integer>(v,i[0]++)).collect(Collectors.toList());}public 
static String join(final int[]a){return Arrays.stream(a).mapToObj(Integer::toString).collect(Collectors.joining(SPACE));
}public static String join(final long[]a){return Arrays.stream(a).mapToObj(Long::toString).collect(Collectors.joining(SPACE));
}public static<T>String join(final T[]a){return Arrays.stream(a).map(v->Objects.toString(v)).collect(Collectors.joining(SPACE));
}public static<T>String join(final T[]a,final Function<T,String>toString){return 
Arrays.stream(a).map(v->toString.apply(v)).collect(Collectors.joining(SPACE));}public 
static<T>String join(final Collection<T>a){return a.stream().map(v->Objects.toString(v)).collect(Collectors.joining(SPACE));
}public static<T>String join(final Collection<T>a,final Function<T,String>toString)
{return a.stream().map(v->toString.apply(v)).collect(Collectors.joining(SPACE));
}public static<T>String join(final Stream<T>a){return a.map(v->Objects.toString(v)).collect(Collectors.joining(SPACE));
}public static<T>String join(final Stream<T>a,final Function<T,String>toString){
return a.map(v->toString.apply(v)).collect(Collectors.joining(SPACE));}public static
<T>String join(final IntStream a){return a.mapToObj(Integer::toString).collect(Collectors.joining(SPACE));
}public static<T>String join(final LongStream a){return a.mapToObj(Long::toString).collect(Collectors.joining(SPACE));
}public static List<Integer>list(final int[]a){return Arrays.stream(a).mapToObj(Integer::valueOf).collect(Collectors.toList());
}public static List<Integer>list(final IntStream a){return a.mapToObj(Integer::valueOf).collect(Collectors.toList());
}public static List<Long>list(final long[]a){return Arrays.stream(a).mapToObj(Long::valueOf).collect(Collectors.toList());
}public static List<Long>list(final LongStream a){return a.mapToObj(Long::valueOf).collect(Collectors.toList());
}public static<T>List<T>list(final Stream<T>a){return a.collect(Collectors.toList());
}public static<T>List<T>list(final Collection<T>a){return a.stream().collect(Collectors.toList());
}public static<T>List<T>list(final T[]a){return Arrays.stream(a).collect(Collectors.toList());
}public static String yesNo(final boolean res){return res?"YES":"NO";}}}
