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 java.util.Scanner;

public class Class {
	private static Scanner in = new Scanner(System.in);

	public static void main(String[] args) {
		int[] doors = new int[26];
		int noOfGuests = in.nextInt();
		int noOfGaurds = in.nextInt();
		int[] guards = new int[26];
		String answer = new String("No");
		String orderOfGuests = in.next();
		for (int i = 0; i < guards.length; i++) {
			guards[i] = Integer.MAX_VALUE;
		}

		for (int i = 0; i < noOfGuests; i++) {
			doors[getOrderOfDoor(orderOfGuests.charAt(i))]++;
		}

		for (int i = 0; i < noOfGuests; i++) {
			if (guards[getOrderOfDoor(orderOfGuests.charAt(i))] != Integer.MAX_VALUE) {
				doors[getOrderOfDoor(orderOfGuests.charAt(i))]--;
				if (doors[getOrderOfDoor(orderOfGuests.charAt(i))] == 0) {
					noOfGaurds++;
					guards[getOrderOfDoor(orderOfGuests.charAt(i))] = Integer.MAX_VALUE;
				}
			} else if (guards[getOrderOfDoor(orderOfGuests.charAt(i))] == Integer.MAX_VALUE && noOfGaurds != 0) {
				noOfGaurds--;
				guards[getOrderOfDoor(orderOfGuests.charAt(i))] = 1;
				doors[getOrderOfDoor(orderOfGuests.charAt(i))]--;
				if (doors[getOrderOfDoor(orderOfGuests.charAt(i))] == 0) {
					noOfGaurds++;
					guards[getOrderOfDoor(orderOfGuests.charAt(i))] = Integer.MAX_VALUE;
				}

			} else if (guards[getOrderOfDoor(orderOfGuests.charAt(i))] == Integer.MAX_VALUE && noOfGaurds == 0) {
				answer = "Yes";
				break;
			}

		}
		System.out.println(answer);

	}

	public static int getOrderOfDoor(char x) {
		return Character.getNumericValue(x) - Character.getNumericValue('A');
	}

}
