import java.io.*;
import java.math.*;
import java.security.*;
import java.text.*;
import java.util.*;
import java.util.concurrent.*;
import java.util.regex.*;

public class Solution {

    // Complete the isValid function below.
    static String isValid(String s) {
        Map<Character,Integer> sMap = new HashMap<Character,Integer>();
        for(int i = 0;i<s.length();i++)
        {
            char x = s.charAt(i);
            if(sMap.containsKey(x))
            {
                sMap.put(x, sMap.get(x)+1);
            }
            else
            {
                sMap.put(x, 1);
            }
        }

        int[] nArr = new int[sMap.size()];
        int i = 0;
        int init = 0;
        boolean flag = false;
        for(Map.Entry<Character,Integer> e : sMap.entrySet())
        {
            nArr[i] = e.getValue();
            if(i ==0)
             init = nArr[i];
            if(Math.abs(nArr[i]-init) ==1)
            {
                    if(flag)
                    {
                        return "NO";
                    }
                    else
                    {
                        flag = true;
                    }
            }
            else if(Math.abs(nArr[i]-init) >1)
            {
                return "NO";
            }
            
            
            i++;
        }
        return "YES";



    }

    private static final Scanner scanner = new Scanner(System.in);

    public static void main(String[] args) throws IOException {
        BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter(System.getenv("OUTPUT_PATH")));

        String s = scanner.nextLine();

        String result = isValid(s);

        bufferedWriter.write(result);
        bufferedWriter.newLine();

        bufferedWriter.close();

        scanner.close();
    }
}