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.*;
import java.util.LinkedList;
import java.util.Objects;
import java.util.StringTokenizer;

public final class Main {
    static char[] chars = {'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'};
    static char[] chars1 = {'#', '*', '&'};
    static char[] chars2 = {'1', '2', '3', '4', '5', '6', '7', '8', '9', '0'};

    static boolean oneColor = true;

    // x1<0
    // x1+k*2>0;
    // k*2>-x1;
    // k=-x1/2
    public void solve() {
        int k = 0;
        String s = in.nextLine();
        for (int i = 0; i < s.length(); i++) {
            char tmp = s.charAt(i);
            int j=0;
            for (; j < chars.length && tmp!=chars[j]; j++);
            if (j>k){
                out.println("NO");
                return;
            }
            if (j==k){
                k++;
            }
        }
        out.println("YES");
    }

    static class Library {
        static boolean isPrime(int a) {
            if (a == 1) {
                return false;
            }
            for (int i = 2; i * i <= a; i++) {
                if (a % i == 0)
                    return false;
            }
            return true;
        }

        static long bpow(long x, long n, long m) {
            long count = 1;
            if (n == 0) {
                return 1;
            }
            while (n > 0) {
                if ((n & 1) == 1) {
                    count *= x;
                    count %= m;
                }
                x *= x;
                x %= m;
                n >>= 1;
            }
            return count % m;
        }

        static long GCD(long a, long b) {
            if (b == 0) return a;
            return GCD(b, a % b);
        }

        static long lcm(long a, long b) {
            return (a * b) / Library.GCD(a, b);
        }
    }

    class Pair<X, Y> implements Comparable<Pair<X, Y>> {

        public X first;
        public Y second;

        public Pair(X first, Y second) {
            this.first = first;
            this.second = second;
        }

        @Override
        public int hashCode() {
            int hash = 7;
            hash = 11 * hash + Objects.hashCode(this.first);
            hash = 11 * hash + Objects.hashCode(this.second);
            return hash;
        }

        @Override
        public boolean equals(Object obj) {
            if (this == obj) {
                return true;
            }
            if (obj == null) {
                return false;
            }
            if (getClass() != obj.getClass()) {
                return false;
            }
            final Pair<?, ?> other = (Pair<?, ?>) obj;
            if (!Objects.equals(this.first, other.first)) {
                return false;
            }
            if (!Objects.equals(this.second, other.second)) {
                return false;
            }
            return true;
        }

        @Override
        public int compareTo(Pair<X, Y> p) {
            return ((Comparable<X>) first).compareTo(p.first);
        }

        @Override
        public String toString() {
            return first + " " + second;
        }
    }

    class Node<E> {
        E element;
        Node<E> left;
        Node<E> right;
        Node<E> prev;

        Node(E element, Node left, Node right, Node prev) {
            this.element = element;
            this.left = left;
            this.right = right;
            this.prev = prev;
        }
    }

    //    -------------I/O-------------    \\
    private FScanner in;

    private PrintWriter out;

    public static void main(String[] args) {
        new Main().runIO();
    }


    void run() {
        try {
            in = new FScanner(new File("input.txt"));
            out = new PrintWriter(new BufferedWriter(new FileWriter(new File("output.txt"))));
            solve();
            out.close();
            in.close();
        } catch (IOException ex) {
            ex.printStackTrace();
        }
    }

    void runIO() {
        in = new FScanner();
        out = new PrintWriter(new BufferedOutputStream(System.out));
        solve();
        out.close();
        in.close();
    }

    class FScanner {

        private BufferedReader br;
        private StringTokenizer st;

        public FScanner() {
            br = new BufferedReader(new InputStreamReader(System.in));
        }

        public FScanner(File f) {
            try {
                br = new BufferedReader(new FileReader(f));
            } catch (FileNotFoundException ex) {
                ex.printStackTrace();
            }
        }

        void useString(String s) {
            if (s != null) {
                st = new StringTokenizer(s);
            }
        }

        void updateST() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

        String next() {
            updateST();
            return st.nextToken();
        }

        Long[] nextLongArray() {
            updateST();
            LinkedList<Long> ll = new LinkedList<>();
            while (st.hasMoreElements()) {
                ll.add(Long.parseLong(st.nextToken()));
            }
            Long[] arr = new Long[1];
            return ll.toArray(arr);
        }

        Integer[] nextIntArray() {
            updateST();
            LinkedList<Integer> ll = new LinkedList<>();
            while (st.hasMoreElements()) {
                ll.add(Integer.parseInt(st.nextToken()));
            }
            Integer[] arr = new Integer[1];
            return ll.toArray(arr);
        }

        int nextInt() {
            return Integer.parseInt(next());
        }

        long nextLong() {
            return Long.parseLong(next());
        }

        double nextDouble() {
            return Double.parseDouble(next());
        }

        String nextLine() {
            updateST();
            StringBuilder sb = new StringBuilder(st.nextToken());
            while (st.hasMoreElements()) {
                sb.append(st.nextToken());
            }
            return sb.toString();
        }

        void close() {
            try {
                br.close();
            } catch (IOException ex) {
                ex.printStackTrace();
            }
        }

    }
}