433 3
FZDDHMJGBZCHFUXBBPIEBBEFDWOMXXEPOMDGSMPIUZOMRZQNSJAVNATGIWPDFISKFQXJNVFXPHOZDAEZFDAHDXXQKZMGNSGKQNWGNGJGJZVVITKNFLVCPMZSDMCHBTVAWYVZLIXXIADXNYILEYNIQHKMOGMVOCWGHCWIYMPEPADSJAAKEGTUSEDWAHMNYJDIHBKHVUHLYGNGZDBULRXLSAJHPCMNWCEAAPYMHDTYWPADOTJTXTXUKLCHWKUSZRHEKQEFPVJEJJHRWCKYOIWALRTIBUMNOCRXLSIKQCJVQXEPGOHRUDJDKMUUUDORURWXJNVRVMNOUNRFKSVMTMZGOIJLXEPAMVGESOADYIGZXRBJDIWKNOWTCSROAQTBECHTOZVSQUOOJRZIBAUHMKAXDCIMDZJFMABGRNTGPUJAUNFPFWCJG
 6 2
ABCABC
 41 19
TMEYYIIELFDCMBDKWWKYNRNDUPRONYROXQCLVQALP
 5 2
ABACA
 377 3
EADADBBBBDEAABBAEBABACDBDBBCACAADBEAEACDEAABACADEEDEACACDADABBBBDDEECBDABACACBAECBADAEBDEEBDBCDAEADBCDDACACDCCEEDBCCBBCEDBECBABCDDBBDEADEDAEACDECECBEBACBCCDCDBDAECDECADBCBEDBBDAAEBCAAECCDCCDBDDEBADEEBDCAEABBDEDBBDDEAECCBDDCDEACDAECCBDDABABEAEDCDEDBAECBDEACEBCECEACDCBABCBAAEAADACADBBBBABEADBCADEBCBECCABBDDDEEBCDEBADEBDAAABBEABADEDEAEABCEEBEEDEAEBEABCEDDBACBCCADEBAAAAAEABABBCE
 3 26
AAB
 27 1
ABCDEFGHIJKLMNOPQRSTUVWXYZA
 73 2
DEBECECBBADAADEAABEAEEEAEBEAEBCDDBABBAEBACCBEEBBAEADEECACEDEEDABACDCDBBBD
 7 2
ABCDBCD
 5 1
AZAZA
 44 15
HGJIFCGGCDGIJDHBIBGAEABCIABIGBDEADBBBAGDFDHA
 5 2
ABCAB
 8 3
ABCBCDCA
 26 1
ABCDEFGHIJKLMNOPQRSTUVWXYZ

YES
 YES
 NO
 NO
 YES
 NO
 YES
 YES
 YES
 YES
 NO
 YES
 NO
 NO



import com.sun.corba.se.impl.orbutil.ORBConstants;
import java.io.PrintWriter;

import java.util.*;
import java.util.Arrays ; 

 
import java.io.DataInputStream; 
import java.io.FileInputStream; 
import java.io.IOException; 
import java.lang.reflect.Array;


public class Test{
     static PrintWriter  pw = new PrintWriter(System.out); 
static class Reader 
    { 
    
        final private int BUFFER_SIZE = 1 << 16; 
        private DataInputStream din; 
        private byte[] buffer; 
        private int bufferPointer, bytesRead; 
  
        public Reader() 
        { 
            din = new DataInputStream(System.in); 
            buffer = new byte[BUFFER_SIZE]; 
            bufferPointer = bytesRead = 0; 
        } 
  
        public Reader(String file_name) throws IOException 
        { 
            din = new DataInputStream(new FileInputStream(file_name)); 
            buffer = new byte[BUFFER_SIZE]; 
            bufferPointer = bytesRead = 0; 
        } 
  
        public String readLine() throws IOException 
        { 
            byte[] buf = new byte[64]; // line length 
            int cnt = 0, c; 
            while ((c = read()) != -1) 
            { 
                if (c == '\n') 
                    break; 
                buf[cnt++] = (byte) c; 
            } 
            return new String(buf, 0, cnt); 
        } 
  
        public int nextInt() throws IOException 
        { 
            int ret = 0; 
            byte c = read(); 
            while (c <= ' ') 
                c = read(); 
            boolean neg = (c == '-'); 
            if (neg) 
                c = read(); 
            do
            { 
                ret = ret * 10 + c - '0'; 
            }  while ((c = read()) >= '0' && c <= '9'); 
  
            if (neg) 
                return -ret; 
            return ret; 
        } 
  
        public long nextLong() throws IOException 
        { 
            long ret = 0; 
            byte c = read(); 
            while (c <= ' ') 
                c = read(); 
            boolean neg = (c == '-'); 
            if (neg) 
                c = read(); 
            do { 
                ret = ret * 10 + c - '0'; 
            } 
            while ((c = read()) >= '0' && c <= '9'); 
            if (neg) 
                return -ret; 
            return ret; 
        } 
  
        public double nextDouble() throws IOException 
        { 
            double ret = 0, div = 1; 
            byte c = read(); 
            while (c <= ' ') 
                c = read(); 
            boolean neg = (c == '-'); 
            if (neg) 
                c = read(); 
  
            do { 
                ret = ret * 10 + c - '0'; 
            } 
            while ((c = read()) >= '0' && c <= '9'); 
  
            if (c == '.') 
            { 
                while ((c = read()) >= '0' && c <= '9') 
                { 
                    ret += (c - '0') / (div *= 10); 
                } 
            } 
  
            if (neg) 
                return -ret; 
            return ret; 
        } 
  
        private void fillBuffer() throws IOException 
        { 
            bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE); 
            if (bytesRead == -1) 
                buffer[0] = -1; 
        } 
  
        private byte read() throws IOException 
        { 
            if (bufferPointer == bytesRead) 
                fillBuffer(); 
            return buffer[bufferPointer++]; 
        } 
  
        public void close() throws IOException 
        { 
            if (din == null) 
                return; 
            din.close(); 
        } 
    } 
   

static int find(long x[],long r){
    int sum =0 ;
    
    for (int i = 0; i < x.length; i++) {
        if(x[i]==r) return i+1 ;
    }
    return sum ;
}
static int [] find2(int x[][],int temp,int y[]){
    for (int i = 0; i < x.length; i++) {
        int sum=0 ;
        for (int j = 0; j < x.length; j++) {
           sum+=x[j][i] ;
        }
        y[i]=sum ;
   
    }
   return y;
    
}
static void found(LinkedList<Integer> l1,String s,LinkedList<Integer> l2){
    for (int i = 0; i < s.length()-1; i++) {
        String temp ="" ;
                temp +=(char)s.charAt(i);
                temp +=(char)s.charAt(i+1);
        if(temp.equals("AB"))l1.add(i) ;
        if(temp.equals("BA"))l2.add(i) ;
    }
}
 static String db(String s){
     StringBuilder b= new StringBuilder(s) ;
     
     return s+(b.reverse().toString()) ; 
    
 }
 static String btw(String s,char c){
     StringBuilder b= new StringBuilder(s) ;
     
     return (s+c)+(b.reverse().toString()) ; 
    
 }

      
      
            


    public static void main(String[] args) throws IOException  {

    
        
  // Reader  in =new Reader ();
  Scanner  in =new Scanner (System.in);
  int n=in.nextInt() ; 
  int k =in.nextInt() ; 
  String s= in.next();
  int []x = new int[26] ; 
  String temp="" ;
  int c=0  ; 
        for (int i = 0; i < s.length(); i++) {
            x[(int)s.charAt(i)-65]++ ;
        }
        for (int i = 0; i < s.length(); i++) {
            
            if(!temp.contains(Character.toString(s.charAt(i)))){
                temp+=s.charAt(i) ; 
                c++ ; 
            }
            System.out.println(temp);
            
            if(c>k){
               System.out.println("YES");
              return ; 
            }
            x[(int)s.charAt(i)-65]-- ;
            if(x[(int)s.charAt(i)-65]==0)c--  ;
        } 
        System.out.println("NO");
        pw.close();
}
}    