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.

/**
 * @author kunal05
 */

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.*;

public class B765 {
	public static void main(String[] args) {
		InputReader in = new InputReader();
		PrintWriter out = new PrintWriter(System.out);
		final long start = System.currentTimeMillis();
		new Task1().solve(in, out);
		final long duration = System.currentTimeMillis()-start;
		out.close();
	}
	
	static class Task1 extends Utility{
		public void solve(InputReader in , PrintWriter out){
			boolean[] marked = new boolean[26];
			String s = in.next();
			
			for(int i=0; i<s.length(); i++){
				for(int j=0; j<26; j++){
					if(s.charAt(i)-'a'>j && !marked[j]){
						out.println("NO");
						return;
					}
				}
				marked[s.charAt(i)-'a'] = true;
			}

			out.println("YES");
		}
	}
	static class InputReader {
		public BufferedReader reader;
		public StringTokenizer tokenizer;
		public InputReader() {
			reader = new BufferedReader(new InputStreamReader(System.in));
			tokenizer = null;
		}
		public String next() {
			while (tokenizer == null || !tokenizer.hasMoreTokens()) {
				try {
					tokenizer = new StringTokenizer(reader.readLine());
				} catch (IOException e) {
					throw new RuntimeException(e);
				}
			}
			return tokenizer.nextToken();
		}
		public int nextInt() {
			return Integer.parseInt(next());
		}
		public long nextLong() {
			return Long.parseLong(next());
		}
		public double nextDouble() {
			return Double.parseDouble(next());
		}
		public String nextLine() {
			String s=null;
			try{
				s = reader.readLine();
			} catch(IOException e){
				throw new RuntimeException(e);
			}
			return s;
        }
		public String nextParagraph() {
			String line=null, ans = "";
			try{
				while ((line = reader.readLine()) != null) {
				ans += line;
				}
			} catch(IOException e){
				throw new RuntimeException(e);
			}
			return ans;
		}	
	}
	static class QuickUnion{
		int[] id;
		int[] size;
		public QuickUnion(int n){
			id = new int[n];
			size = new int[n];
			for(int i=0; i<n; i++){
				id[i] = i;
				size[i] = 1;
			}
		}
		public int root(int a){
			while(a!=id[a]){
				id[a] = id[id[a]];
				a = id[a];
			}
			return a;
		}
		public boolean connected(int p, int q){
			return root(p)==root(q);
		}
		public void union(int p, int q){
			int pid = root(p);
			int qid = root(q);
			if(pid==qid) return;
			if(size[pid]>=size[qid]){
				size[pid] += size[qid];
				id[qid] = pid;
			} else {
				size[qid] += size[pid];
				id[pid] = qid;
			}
		}
	}
	static class Utility{
		static final int MOD = 1000000007;
		long expo(long a, long b){
			long result = 1;
			while (b>0){
				if (b%2==1) result=(result*a)%MOD;
				b>>=1;
				a=(a*a)%MOD;
			}
			return result%MOD;
		}
		long fibonacci(long n){
			if(n==0) return 0;
			long a=0, b=1, c=1, d=1, e=n-2;
			long a1, b1, c1, d1, a2=0, b2=1, c2=1, d2=1;
			
			while(e>0){
				if(e%2==1){
					a1 = (a*a2+b*c2)%MOD;
					c1 = (c*a2+d*c2)%MOD;
					b1 = (a*b2+ b*d2)%MOD;
					d1 = (b2*c+ d*d2)%MOD;
					a=a1; b=b1; c=c1; d= d1;
				}
				a1 = (a2*a2+b2*c2)%MOD;
				c1 = (c2*a2+d2*c2)%MOD;
				b1 = (a2*b2+ b2*d2)%MOD;
				d1 = (b2*c2+ d2*d2)%MOD;
				a2=a1; b2=b1; c2=c1; d2= d1;
				e /= 2;
			}
			return d;
		}
		long gcd(long a, long b){
			long mod = b%a;
			while(mod!=0){
				b=a;
				a=mod;
				mod=b%a;
			}
			return a;
		}
		long inverseModullo(long numerator, long denominator){
			return ((numerator%MOD)*(expo(denominator, MOD-2)))%MOD;
		}
	}
	static class KMP {
		private static final int R = 256;		//radix
		private int M;
		private String pat;
		private int[][] dfa;
		public KMP(String pattern){
			this.pat = pattern;
			M = pat.length();
			dfa = new int[R][M];
			dfa[pat.charAt(0)][0] = 1;
			for(int X=0, j=1; j<M; j++){
				for(int c=0; c<R; c++)
					dfa[c][j] = dfa[c][X];		//copy mismatch cases
				dfa[pat.charAt(j)][j] = j+1;	//set match case
				X = dfa[pat.charAt(j)][X];		//update restart state
			}
		}
		public int search(String txt){
			int i,j, N = txt.length();
			for(i=0, j=0; i<N && j<M; i++)
				j = dfa[txt.charAt(i)][j];
			if(j==M) return i-M;
			else return N;
		}
	}
}